MIPS: Clean-up GIC and vectored interrupts.

This change adds macros for routing of GIC interrupts for EIC and
non-EIC hardware modes. Also added Malta GIC macros having to do
with performance and timer interrupts.

Signed-off-by: Steven J. Hill <sjhill@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3576/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>