serial: msm_geni_serial: Allow clock_on/off ioctl to be optional

Add support in the driver to manage power without enabling pm runtime.
UART driver gives control to user space client to vote for clock on/off
by exposing ioctls. These vote clock on/off APIs depend on PM runtime
framework for power related operations.

This change relaxes driver from depending on userspace ioctls to invoke
runtime resume/suspend for basic uart functionality which will now be
done by system suspend/resume. This will block PM framework API's and use
system suspend/resume API for UART on/off.

Change-Id: Idf0632c0e2d40907f7a226cd7e3e814d1c1f6751
Signed-off-by: Ashish Kori <akori@codeaurora.org>