staging: fsl-mc: allow the driver compile multi-arch

Add an alternate dependency on COMPILE_TEST, thus leaving
this driver compile on other architectures.
Also, other drivers depending on the bus are updated to depend
on ARCH_LAYERSCAPE until they'll also be made multi-arch.
This was compiled tested on:
 - booke powerpc (corenet{32,64}_smp_defconfig)
 - x86 (i386_defconfig, x86_64_defconfig, needs CONFIG_OF)
 - arm64 (defconfig)

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>