Build: Add some missing files in NS build

Install multi-core header files into a dedicated folder.
Install platform common include and crypto key header files.

Change-Id: Ifd6314ddd59205c0e3fc3ae07aaad4205e1f542b
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/cmake/spe-CMakeLists.cmake b/cmake/spe-CMakeLists.cmake
index 6b72e67..15e392d 100644
--- a/cmake/spe-CMakeLists.cmake
+++ b/cmake/spe-CMakeLists.cmake
@@ -30,6 +30,7 @@
 target_include_directories(tfm_api_ns
     PUBLIC
         interface/include
+        interface/include/crypto_keys
 )
 
 add_subdirectory(platform)