common.mk: set CFG_USER_TA_TARGETS

Sets CFG_USER_TA_TARGETS to ta_arm32 or ta_arm64 based on COMPILE_S_USER
to match the used TA devkit. This avoids problems with in-tree TAs like
pkcs11_ta being compiled for a different TA devkit than what is used by
buildroot to populate the rootfs.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/common.mk b/common.mk
index c0929f4..937e9c9 100644
--- a/common.mk
+++ b/common.mk
@@ -201,9 +201,11 @@
 
 ifeq ($(COMPILE_S_USER),32)
 OPTEE_OS_TA_DEV_KIT_DIR	?= $(OPTEE_OS_PATH)/out/arm/export-ta_arm32
+OPTEE_OS_COMMON_EXTRA_FLAGS	+= CFG_USER_TA_TARGETS=ta_arm32
 endif
 ifeq ($(COMPILE_S_USER),64)
 OPTEE_OS_TA_DEV_KIT_DIR	?= $(OPTEE_OS_PATH)/out/arm/export-ta_arm64
+OPTEE_OS_COMMON_EXTRA_FLAGS	+= CFG_USER_TA_TARGETS=ta_arm64
 endif
 
 ifeq ($(COMPILE_S_KERNEL),64)