MIPS: CPS: Use change_*, set_* & clear_* where appropriate

MIPS: CPS: Use change_*, set_* & clear_* where appropriate

Make use of the new change_*, set_* & clear_* accessor functions for CPS
(CM, CPC & GIC) registers where doing so makes the code easier to read
or shortens it without adversely affecting readability.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17005/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>