pwm qmsi: Add suspend/resume

Implement saving and restoring context of the PWM controller when the
application goes to SYS_PM_DEEP_SLEEP. No action is taken for other
states at the moment.

This functionality is implemented in the shim driver first to enable
the feature, but will later be moved into QMSI.

Change-Id: I5784f6a2c63caaea5785ca5d92bb6cc3bc9fa4cc
Signed-off-by: Iván Briano <ivan.briano@intel.com>