TTY: msm_smd_tty: Fix client notification issue in suspend state

SMD_TTY driver holds a wakeup source for 500ms to provide enough time
to notify the user client waiting for data. However, when system is in
suspend state the 500ms timer may not be sufficient to notify the
user clients because in some cases system resume of devices and tasks
is taking more time and this causes delay in client notification.

Register for PM_SUSPEND_PREPARE and PM_POST_SUSPEND events to track
system suspend and resume state and then notify the clients after system
resume completes.

CRs-Fixed: 613589
Change-Id: Iffb2ecb1c58f46e0c4a745cdcce2fb717ea2ece8
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>