MIPS: Add MSI support for XLP9XX

MIPS: Add MSI support for XLP9XX

In XLP9XX, the interrupt routing table for MSI-X has been moved to the
PCIe controller's config space from PIC. There are also 32 MSI-X
interrupts available per link on XLP9XX.

Update XLP MSI/MSI-X code to handle this.

Signed-off-by: Ganesan Ramalingam <ganesanr@broadcom.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: g@linux-mips.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6912/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>