msm: iomap: Add mappings for the MPM PS_HOLD region

A static mapping is needed for PS_HOLD for increased
robustness of the restart code, especially during a kernel
panic.

Change-Id: I616d1a27024120a4c53d8dbc524c4c38349dc704
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>