fsl_rio: fix compile errors

Fixes the following compile problem on E500 platforms:
arch/powerpc/sysdev/fsl_rio.c: In function 'fsl_rio_mcheck_exception':
arch/powerpc/sysdev/fsl_rio.c:248: error: 'MCSR_MASK' undeclared (first use in this function)

Also fixes the compile problem on non-E500 platforms.

Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>