uart_qmsi: Implement suspend and resume functions

In order to restore uart context after entering
SYS_PM_DEEP_SLEEP, suspend and resume functions
are called.

The following parameters are restored:
 - All registers for the UART device.
 - UART clocks.

The FIFO control register cannot be read back and is
not stored in the device configuration.
The default parameters are applied for them.

The suspend/resume functionality is implemented in
the QMSI shim layer as a fast and temporary solution,
it will be removed and migrated to QMSI later.

Change-Id: I4be9246f6aa5a6e0d91df54c1c69574060136607
Signed-off-by: Julien Delayen <julien.delayen@intel.com>