powerpc/fsl_msi: Add multiple MSI bank support

Freescale QorIQ P4080 has three MSI banks and the original code
can not work well. This patch adds multiple MSI banks support for
Freescale processor.

Signed-off-by: Lan Chunhe-B25806 <b25806@freescale.com>
Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>