BL2: use regex instead of external config.py

Using 'config.py' would require the framework submodule to be available
in tf-psa-crypto, which might not always be the case (ex: Zephyr). This
commit replaces that script with a regex check to verify if the P256-M
driver is enabled or not in the BL2's configuration file.

Change-Id: Idcbb66086b891cb22c53bf4ebcdba10331bf7ebf
Signed-off-by: Valerio Setti <vsetti@baylibre.com>

Author: valeriosetti

bl2/CMakeLists.txt

@@ -45,19 +45,14 @@ target_include_directories(bl2_crypto_config
 
 # Check if the p256m driver is enabled in the config file, as that will require
 # to build some 3rd party specific source code in addition to TF-PSA-Crypto source.
-# Note that 0 means SUCCESS here, 1 means FAILURE
-set(MBEDTLS_P256M_NOT_FOUND 1)
-execute_process(COMMAND
-    ${Python3_EXECUTABLE}
-    ${TF_PSA_CRYPTO_PATH}/scripts/config.py -f "${MCUBOOT_PSA_CRYPTO_CONFIG_FILEPATH}" get MBEDTLS_PSA_P256M_DRIVER_ENABLED
-    RESULT_VARIABLE MBEDTLS_P256M_NOT_FOUND)
-
-# If the enablement is conditional, the script would still mark it as found
-if (${MBEDTLS_P256M_NOT_FOUND} EQUAL 0)
+file(STRINGS "${MCUBOOT_PSA_CRYPTO_CONFIG_FILEPATH}" _p256m_line
+    REGEX "^[ \t]*#define[ \t]+MBEDTLS_PSA_P256M_DRIVER_ENABLED")
+if(_p256m_line)
     set(MBEDTLS_P256M_ENABLED true)
 else()
     set(MBEDTLS_P256M_ENABLED false)
 endif()
+message(VERBOSE "BL2 using P256-M driver: ${MBEDTLS_P256M_ENABLED}")
 
 ############################### BL2_CRYPTO #####################################