MIPS: CM: make use of mips_cm_{lock,unlock}_other

Document that CPC core-other accesses must take place within the bounds
of the CM lock, and begin using the CM lock functions where we access
the GCRs of other cores. This is required because with CM3 the CPC began
using GCR_CL_OTHER instead of CPC_CL_OTHER.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-kernel@vger.kernel.org
Cc: Niklas Cassel <niklas.cassel@axis.com>
Cc: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/11208/


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