MIPS: CM: The CMGCRBase register is 64-bit on 64 bit kernels.

The CMGCRBase register (CP0, 15, 3) register is 64-bit on MIPS64
so we change its type to unsigned long.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10644/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>