MIPS: smp-cps: use CPC core-other locking

MIPS: smp-cps: use CPC core-other locking

The core which the CPC core-other region relates to is based upon the
core-local core-other addressing register. As its name suggests this
register is shared between all VPEs within a core, and if there is a
possibility that multiple VPEs within a core will attempt to access
another core simultaneously then locking is required. This wasn't
previously a problem with the only user being cpu0 during boot, but will
be an issue once hotplug is implemented & may race with other users such
as cpuidle.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>