MIPS: Add MIPS P5600 probe support

Add a case in cpu_probe_mips for the MIPS P5600 processor ID, which sets
the CPU type to the new CPU_P5600.

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/6409/


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