MIPS: Add MIPS I6400 probe support

Add a case in cpu_probe_mips for the MIPS I6400 processor ID, which sets
the CPU type to the new CPU_I6400.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10636/


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