msm: kgsl: Map powerup register list as coherent privileged RW memory

Map powerup register list global buffer as coherent privileged RW memory
because it contains a software spinlock used by both CPU and CP to
synchronize registers to restore after preemption and interframe power
collapse. For software spinlock to work correctly order or read/writes
is important so this memory needs to be mapped as coherent memory.

Change-Id: Ieff60d4e249ff62089c1ed723851b79991d417ba
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>