tty: serial: qcom_geni_serial: Fix softlock

Transfers were being divided into device FIFO sized (64 byte max)
operations which would poll for completion within a spin_lock_irqsave /
spin_unlock_irqrestore block. This both made things slow by waiting for
the FIFO to completely drain before adding further data and would also
result in softlocks on large transmissions.

This patch allows larger transfers with continuous FIFO additions as
space becomes available and removes polling from the interrupt handler.

Change-Id: I9225c86482550ca9f7433a585fdd0e4edf1b2f87
Signed-off-by: Ryan Case <ryandcase@chromium.org>
Git-commit: a1fee899e5bed457afc20a6a2ff3915a95cc5942
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[msavaliy@codeaurora.org: Applied patch to downstream file - msm_geni_serial.c]
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>