serial: msm_geni_serial: Prevent Rx lockup and Tx truncations

Don't touch the Rx related packing or stale registers while the Rx state
machine is running, this could lead to the Rx sequencer to be in an
unusual state preventing any further Rx operations.
Signal the framework when there fewer than wakeup characters left in
the xmit buffer else there are some characters lost during Tx.
Vote on the resources prior to resuming the port else this could lead to
bus errors.

Change-Id: I6432d6d7798d302abcbc58d985ab8ed129c37937
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>