powerpc/fsl_msi: enable msi sharing through AMP OSes

Make a single PCIe MSI bank shareable through CAMP OSes. The number of
MSI used by each core can be configured by dts file.

Signed-off-by: Zhao Chenhui <b26998@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>