Build: Add support for PSA API tests for ITS

Updates the CMake files to make it possible to link against the
PSA API tests for ITS and makes corresponding updates to the build
instructions.

Change-Id: Ic61788e7253be623cb5da1c2631ebc720be0892f
Signed-off-by: Jamie Fox <jamie.fox@arm.com>
diff --git a/CommonConfig.cmake b/CommonConfig.cmake
index 5b69392..7557293 100644
--- a/CommonConfig.cmake
+++ b/CommonConfig.cmake
@@ -269,6 +269,9 @@
 	if (NOT DEFINED PSA_API_TEST_CRYPTO)
 		set(PSA_API_TEST_CRYPTO OFF)
 	endif()
+	if (NOT DEFINED PSA_API_TEST_INTERNAL_TRUSTED_STORAGE)
+		set(PSA_API_TEST_INTERNAL_TRUSTED_STORAGE OFF)
+	endif()
 	if (NOT DEFINED PSA_API_TEST_SECURE_STORAGE)
 		set(PSA_API_TEST_SECURE_STORAGE OFF)
 	endif()