MIPS: Add cases for CPU_P5600

Add a CPU_P5600 case to various switch statements, doing the same thing
as for CPU_PROAPTIV.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6408/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>