arm: Prevent redefinition error in fsl-layerscape

The include/phy.h will start including dm.h, which pulls in
linux/compat.h after the attempted redefinition in
arch/arm/include/asm/armv8/mmu.h, so move this include to allow
redefinition.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>