usb: chipidea: add ci_hdrc_enter_lpm API

usb: chipidea: add ci_hdrc_enter_lpm API

This API is used to let the PHY enter/leave low power mode.
Before the controller going to work(at probe/resume), it needs to let
the PHY leave low power mode.
After the controller stopping working(at remove/suspend), it needs to
let the PHY enter low power mode to save power consumption.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>