Platform: Add arm folder for arm platforms

Put arm platforms into arm folder and remove some unused
cryptocell-312-runtime. It will be convenient for users and
developers.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I1187a8f2b18903e531ce28b2d23be251ec1e2b45
diff --git a/docs/technical_references/profiles/tfm_profile_large.rst b/docs/technical_references/profiles/tfm_profile_large.rst
index 2e0bc76..89edd29 100644
--- a/docs/technical_references/profiles/tfm_profile_large.rst
+++ b/docs/technical_references/profiles/tfm_profile_large.rst
@@ -407,7 +407,7 @@
 
    cd <TFM root dir>
    mkdir build && cd build
-   cmake -DTFM_PLATFORM=mps2/an521 \
+   cmake -DTFM_PLATFORM=arm/mps2/an521 \
          -DTFM_TOOLCHAIN_FILE=../toolchain_ARMCLANG.cmake \
          -DTFM_PROFILE=profile_large \
          -DCMAKE_BUILD_TYPE=MinSizeRel \
@@ -421,7 +421,7 @@
 
    cd <TFM root dir>
    mkdir build && cd build
-   cmake -DTFM_PLATFORM=mps2/an521 \
+   cmake -DTFM_PLATFORM=arm/mps2/an521 \
          -DTFM_TOOLCHAIN_FILE=../toolchain_ARMCLANG.cmake \
          -DTFM_PROFILE=profile_large \
          -DCMAKE_BUILD_TYPE=MinSizeRel \
diff --git a/docs/technical_references/profiles/tfm_profile_medium.rst b/docs/technical_references/profiles/tfm_profile_medium.rst
index ab552f1..ae24b98 100644
--- a/docs/technical_references/profiles/tfm_profile_medium.rst
+++ b/docs/technical_references/profiles/tfm_profile_medium.rst
@@ -430,7 +430,7 @@
 
    cd <TFM root dir>
    mkdir build && cd build
-   cmake -DTFM_PLATFORM=mps2/an521 \
+   cmake -DTFM_PLATFORM=arm/mps2/an521 \
          -DTFM_TOOLCHAIN_FILE=../toolchain_ARMCLANG.cmake \
          -DTFM_PROFILE=profile_medium \
          -DCMAKE_BUILD_TYPE=MinSizeRel \
@@ -444,7 +444,7 @@
 
    cd <TFM root dir>
    mkdir build && cd build
-   cmake -DTFM_PLATFORM=mps2/an521 \
+   cmake -DTFM_PLATFORM=arm/mps2/an521 \
          -DTFM_TOOLCHAIN_FILE=../toolchain_ARMCLANG.cmake \
          -DTFM_PROFILE=profile_medium \
          -DCMAKE_BUILD_TYPE=MinSizeRel \
diff --git a/docs/technical_references/profiles/tfm_profile_small.rst b/docs/technical_references/profiles/tfm_profile_small.rst
index d95d693..a97a1e1 100644
--- a/docs/technical_references/profiles/tfm_profile_small.rst
+++ b/docs/technical_references/profiles/tfm_profile_small.rst
@@ -584,7 +584,7 @@
 
    cd <TFM root dir>
    mkdir build && cd build
-   cmake -DTFM_PLATFORM=mps2/an521 \
+   cmake -DTFM_PLATFORM=arm/mps2/an521 \
          -DTFM_TOOLCHAIN_FILE=../toolchain_ARMCLANG.cmake \
          -DTFM_PROFILE=profile_small \
          -DCMAKE_BUILD_TYPE=MinSizeRel \
@@ -598,7 +598,7 @@
 
    cd <TFM root dir>
    mkdir build && cd build
-   cmake -DTFM_PLATFORM=mps2/an521 \
+   cmake -DTFM_PLATFORM=arm/mps2/an521 \
          -DTFM_TOOLCHAIN_FILE=../toolchain_ARMCLANG.cmake \
          -DTFM_PROFILE=profile_small \
          -DCMAKE_BUILD_TYPE=MinSizeRel \
diff --git a/docs/technical_references/tfm_secure_boot.rst b/docs/technical_references/tfm_secure_boot.rst
index 1907cea..61bdcb5 100644
--- a/docs/technical_references/tfm_secure_boot.rst
+++ b/docs/technical_references/tfm_secure_boot.rst
@@ -309,7 +309,7 @@
 
 Example of how to provide the secure image minimum version::
 
-    cmake -DTFM_PLATFORM=musca_b1/sse_200 -DMCUBOOT_S_IMAGE_MIN_VER=1.2.3+4 ..
+    cmake -DTFM_PLATFORM=arm/musca_b1/sse_200 -DMCUBOOT_S_IMAGE_MIN_VER=1.2.3+4 ..
 
 ********************
 Signature algorithms
@@ -427,7 +427,7 @@
 The version number of the image (single image boot) can manually be passed in
 through the command line in the cmake configuration step::
 
-    cmake -DTFM_PLATFORM=musca_b1/sse_200 -DIMAGE_VERSION_S=1.2.3+4 ..
+    cmake -DTFM_PLATFORM=arm/musca_b1/sse_200 -DIMAGE_VERSION_S=1.2.3+4 ..
 
 Alternatively, the version number can be less specific (e.g 1, 1.2, or 1.2.3),
 where the missing numbers are automatically set to zero. The image version
@@ -461,7 +461,7 @@
 current image version. The value of the security counter (single image boot) can
 be specified at build time in the cmake configuration step::
 
-    cmake -DTFM_PLATFORM=musca_b1/sse_200 -DSECURITY_COUNTER_S=42 ../
+    cmake -DTFM_PLATFORM=arm/musca_b1/sse_200 -DSECURITY_COUNTER_S=42 ../
 
 The security counter can be independent from the image version, but not
 necessarily. Alternatively, if it is not specified at build time with the