msm: adsprpc: Protect maps using map mutex

Protect maps using map mutex as well as avoid
deadlock during SSR in case of legacy targets.

Change-Id: Ia972302a8830d501c40d06df79e7eb305327c5ad
Acked-by: Deepika Singh <dsi@qti.qualcomm.com>
Signed-off-by: Jeya R <jeyr@codeaurora.org>