MIPS: Remove gcmpregs.h

This header was used only by Malta but is used no longer. Remove it. It
was also included unnecessarily in irq-gic.c, so that include is also
removed.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6366/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>