fix(plat/imx/imx8m/imx8mm): fix FTBFS on SPD=opteed

We need to add #include <arch.h> to platform_def.h to fix MODE_RW_64
undeclared.

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Change-Id: I358bc6644243a7ea1befd87f946b4087feddd857

plat/imx/imx8m/imx8mm/include/platform_def.h

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
+#include <arch.h>
 #include <common/tbbr/tbbr_img_def.h>
 
 #define PLATFORM_LINKER_FORMAT		"elf64-littleaarch64"