soc: qcom: glink_smd_xprt: Make poll() atomic

A Glink client requires that the poll processing be atomic and cannot
tolerate a context switch.  Change the poll() implementation so that packet
processing is done on the calling context.

Change-Id: If1c67ac17a3f0f523b4d596675a055b3e879217b
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>