staging: fsl-mc/dpio: allow the driver to compile multi-arch

Drop dependency on ARCH_LAYERSCAPE (which in turn depends on ARM64),
thus allowing this driver to compile on all architectures supported
by the fsl-mc bus driver.

This was compile tested on:
 - powerpc (corenet_basic_defconfig, ppc64_defconfig)
 - x86 (i386_defconfig, x86_64_defconfig, needs CONFIG_OF)
 - arm64 (defconfig)

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>