powerpc/fsl_msi: add MSIIR1 support for MPIC v4.3

powerpc/fsl_msi: add MSIIR1 support for MPIC v4.3

The original MPIC MSI bank contains 8 registers, MPIC v4.3 MSI bank
contains 16 registers, and this patch adds NR_MSI_REG_MAX and
NR_MSI_IRQS_MAX to describe the maximum capability of MSI bank.
MPIC v4.3 provides MSIIR1 to index these 16 MSI registers. MSIIR1
uses different bits definition than MSIIR. This patch adds
ibs_shift and srs_shift to indicate the bits definition of the
MSIIR and MSIIR1, so the same code can handle the MSIIR and MSIIR1
simultaneously.

Signed-off-by: Minghuan Lian <Minghuan.Lian@freescale.com>
[scottwood@freescale.com: reinstated static on all_avail]
Signed-off-by: Scott Wood <scottwood@freescale.com>