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
1 file changed