ta/crypt: add TA_CRYPT_CMD_MBED_SELF_TESTS

Adds the TAF TA_CRYPT_CMD_MBED_SELF_TESTS which calls mbedTLS self tests if
compiled with CFG_TA_MBEDTLS_SELF_TEST

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/ta/crypt/sub.mk b/ta/crypt/sub.mk
index 83286c2..94ebbb2 100644
--- a/ta/crypt/sub.mk
+++ b/ta/crypt/sub.mk
@@ -5,3 +5,4 @@
 srcs-y += sha2_impl.c
 srcs-y += sha2_taf.c
 srcs-y += ta_entry.c
+srcs-$(CFG_TA_MBEDTLS) += mbedtls_taf.c