Fix musb suspend behavior

- Add pm_ops to the MTK MUSB platform glue. In these, we enable/disable
the USB clocks and PHY. This gives us a nice behavior where the USB
device disconnects cleanly from the host machine, and then re-connects
when it exits suspend (previous behavior disconnected, and then tried
really hard to reconnect, but there was no one home.)

Change-Id: If975fcd2a7e1332f120c3f8997e81e21fd43c5cb