msm_serial_hs: Track TX transmit time and detect errors

The time taken to complete TX data transmission
from the UART hardware FIFOs are tracked, so that,
the tranmsission errors due to the remote entity disabling
the flow control line for unusually long duration are
tracked and logged.

Change-Id: I4f85aff2801f90add8c9d01a2f0b870fb91ab898
Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>