msm: smd: fix packet polling race condition

Packet polling is intended to be used with interrupts disabled, however in
multicore targets, interrupts may not be disabled on all cores.  Therefore
packet polling must lock on shared resources to ensure cores with
interrupts enabled do not stomp on polling operations.

Change-Id: I2faa1024024a46ef7c55224f8e9c5e548d07c5e4
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>