USB: Allow skipping device resume during system resume

This allows xHC to remain in low power mode and not
resume the bus when system wide resume happens.
Controller comes out of low power mode only when usb
device issues a remote wakeup or if there is a host
initiated bus resume.

Change-Id: I96cdcb9e3642906b4afa08d9bde07e123d9b3977
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>