USB: OTG: msm: Add support for power management

Implement runtime and system pm ops to put hardware into low power
mode (LPM). As part of LPM, USB clocks are turned off, PHY is put
into suspend state and PHY comparators are turned off if VBUS/Id
notifications are not required from PHY.

Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>