msm: rpc: add shutdown and restart handler for rpc

Add shutdown and restart handler for rpcrouter. The
shutdown handler take care of calling the
msm_rpcrouter_close function with a pre defined
priority. PM no longer handle rpc close in the shutdown/reboot
sequence.

CRs-fixed: 396641
Change-Id: I83d4bbe759b573cb0d9d9b2c8d3d1d907ec297d5
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Signed-off-by: Angshuman Sarkar <angshuman@codeaurora.org>