Migrate ARM platforms to use TF_MBEDTLS_KEY_ALG

A previous patch superseded the MBEDTLS_KEY_ALG. This patch updates
the ARM platforms to use the new TF_MBEDTLS_KEY_ALG define.

Change-Id: Ie0e1bc272e127e879ac58e7cfcbe268751d7688e
Signed-off-by: David Cunado <david.cunado@arm.com>

plat/arm/common/arm_common.mk

@@ -171,7 +171,7 @@ ifneq (${TRUSTED_BOARD_BOOT},0)
 
     $(eval $(call FWU_FIP_ADD_IMG,NS_BL2U,--fwu))
 
-    MBEDTLS_KEY_ALG	:=	${KEY_ALG}
+    TF_MBEDTLS_KEY_ALG	:=	${KEY_ALG}
 
     # We expect to locate the *.mk files under the directories specified below
     CRYPTO_LIB_MK := drivers/auth/mbedtls/mbedtls_crypto.mk