uart: qmsi: Adds device suspend/resume to uart_qmsi device

This adds some basic suspend/resume support in the uart_qmsi
driver. This is part of a change to enable device suspend/resume
and deep sleep support in sample PM application.

Jira: ZEP-512
Change-Id: I38cfbfb352d0027b7beaadebedbc10002dade50a
Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>