msm: tty: update receive room just before writing data to the ldisc

There is a corner case in the tty driver where the value of
tty->receive_room is not being updated before writing data to
the line discipline. When this happens, data is lost because
of failure to re-submit any remaining data to the ldisc.

This fix is dependent on a new tty flag that is set only when
the tty driver is used for efs sync betweem the mdm modem and
the applications processor.

CRs-Fixed: 358868
Change-Id: I0ba02980504b4d8187b8c83111c2c883d194efa2
Signed-off-by: Joel King <joelking@codeaurora.org>