usb: gadget: hsic: Disable usb_hsic_xcvr_clk when entering low power mode

HSIC core driver is missing disabling and upreparing the usb_hsic_xcvr_clk
clock when it enters into low-power mode. Added a call to clock disable and
upreparing API on low-power mode entry and clock enable and preparing API
on low-power mode exit for this clock. This allows saving extra power and
TCXO shutdown.

Change-Id: I2c822e15b13b76f340e936f62044058c53874328
Signed-off-by: Danny Segal <dsegal@codeaurora.org>