Build: Improve dependency version handling

Add version variable for tf-m-tests, and update handling so that the
version variable always corresponds exactly to the git tag/hash/branch

Change-Id: Id4fe50487c599b12640704eb1bde79117c79db19
Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/lib/ext/mbedcrypto/CMakeLists.txt b/lib/ext/mbedcrypto/CMakeLists.txt
index 828a188..79adce1 100644
--- a/lib/ext/mbedcrypto/CMakeLists.txt
+++ b/lib/ext/mbedcrypto/CMakeLists.txt
@@ -20,7 +20,7 @@
     if (PATCH_FILES)
         FetchContent_Declare(mbedcrypto
             GIT_REPOSITORY https://github.com/ARMmbed/mbedtls.git
-            GIT_TAG mbedtls-${MBEDCRYPTO_VERSION}
+            GIT_TAG ${MBEDCRYPTO_VERSION}
             GIT_SHALLOW TRUE
             GIT_PROGRESS TRUE
             GIT_SUBMODULES ""
@@ -29,7 +29,7 @@
     else()
         FetchContent_Declare(mbedcrypto
             GIT_REPOSITORY https://github.com/ARMmbed/mbedtls.git
-            GIT_TAG mbedtls-${MBEDCRYPTO_VERSION}
+            GIT_TAG ${MBEDCRYPTO_VERSION}
             GIT_SHALLOW TRUE
             GIT_PROGRESS TRUE
             GIT_SUBMODULES ""
diff --git a/lib/ext/tf-m-tests/CMakeLists.txt b/lib/ext/tf-m-tests/CMakeLists.txt
index 3a1e60d..b26a0fd 100644
--- a/lib/ext/tf-m-tests/CMakeLists.txt
+++ b/lib/ext/tf-m-tests/CMakeLists.txt
@@ -16,6 +16,7 @@
 if ("${TFM_TEST_REPO_PATH}" STREQUAL "DOWNLOAD")
     FetchContent_Declare(tfm_test_repo
         GIT_REPOSITORY https://git.trustedfirmware.org/TF-M/tf-m-tests.git
+        GIT_TAG ${TFM_TEST_REPO_VERSION}
         GIT_SHALLOW TRUE
         GIT_PROGRESS TRUE
     )