MIPS: smp-cps: flush cache after patching mips_cps_core_entry

MIPS: smp-cps: flush cache after patching mips_cps_core_entry

The start of mips_cps_core_entry is patched in order to provide the code
with the address of the CM register region at a point where it will be
running non-coherent with the rest of the system. However the cache
wasn't being flushed after that patching which could in principle lead
to secondary cores using an invalid CM base address.

The patching is moved to cps_prepare_cpus since local_flush_icache_range
has not been initialised at the point cps_smp_setup is called.

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