Build: Search platform folders by cpuarch.cmake instead

Change-Id: I16719478eb448fc5406af4c455e5348251f1da1d
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
diff --git a/config/tfm_platform.cmake b/config/tfm_platform.cmake
index 469cc57..345ad29 100644
--- a/config/tfm_platform.cmake
+++ b/config/tfm_platform.cmake
@@ -10,10 +10,10 @@
 if (NOT IS_ABSOLUTE "${TFM_PLATFORM}" AND NOT IS_DIRECTORY "${TARGET_PATH}/${TFM_PLATFORM}")
     # If TFM_PLATFORM is not a relative patch to ${TARGET_PATH}, then it could
     # be a platform name, for example an521. Search directories which contain
-    # the "preload.cmake" and find the the match one.
+    # the "cpuarch.cmake" and find the the match one.
 
-    # Get the list of directories which have preload.cmake
-    file(GLOB_RECURSE PLATFORM_PATHS ${TARGET_PATH} "preload.cmake")
+    # Get the list of directories which have cpuarch.cmake
+    file(GLOB_RECURSE PLATFORM_PATHS ${TARGET_PATH} "cpuarch.cmake")
 
     # Search the list with platform name and store the result in PLATFORM_PATHS
     list(FILTER PLATFORM_PATHS INCLUDE REGEX "/${TFM_PLATFORM}/")