Add support for TBBR using ECDSA keys in ARM platforms

    - fixed compile error when KEY_ALG=ecdsa
    - add new option ecdsa for TF_MBEDTLS_KEY_ALG
    - add new option devel_ecdsa for ARM_ROTPK_LOCATION
    - add ecdsa key at plat/arm/board/common/rotpk/
    - reduce the mbedtls heap memory size to 13k

Change-Id: I3f7a6170af93fdbaaa7bf2fffb4680a9f6113c13
Signed-off-by: Qixiang Xu <qixiang.xu@arm.com>
diff --git a/drivers/auth/mbedtls/mbedtls_common.c b/drivers/auth/mbedtls/mbedtls_common.c
index e9aa409..cc57af3 100644
--- a/drivers/auth/mbedtls/mbedtls_common.c
+++ b/drivers/auth/mbedtls/mbedtls_common.c
@@ -15,7 +15,7 @@
  * mbed TLS heap
  */
 #if (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_ECDSA)
-#define MBEDTLS_HEAP_SIZE		(14*1024)
+#define MBEDTLS_HEAP_SIZE		(13*1024)
 #elif (TF_MBEDTLS_KEY_ALG_ID == TF_MBEDTLS_RSA)
 #define MBEDTLS_HEAP_SIZE		(7*1024)
 #endif