chore(imx): remove duplicate define

Signed-off-by: Jimmy Brisson <jimmy.brisson@arm.com>
Change-Id: If55d4e2777ca2cdcf55da3b2a60d99f694a2c94d
diff --git a/plat/imx/imx8m/imx8mm/platform.mk b/plat/imx/imx8m/imx8mm/platform.mk
index f0cdb3e..d1c1259 100644
--- a/plat/imx/imx8m/imx8mm/platform.mk
+++ b/plat/imx/imx8m/imx8mm/platform.mk
@@ -188,10 +188,6 @@
     $(info Including ${MEASURED_BOOT_MK})
     include ${MEASURED_BOOT_MK}
 
-ifneq (${MBOOT_EL_HASH_ALG}, sha256)
-    $(eval $(call add_define,TF_MBEDTLS_MBOOT_USE_SHA512))
-endif
-
 BL2_SOURCES		+=	plat/imx/imx8m/imx8m_measured_boot.c	\
 				plat/imx/imx8m/imx8m_dyn_cfg_helpers.c	\
 				${EVENT_LOG_SOURCES}