usb: hsic: Add USB HSIC clock unvoting in low-power mode

When the HSIC core enters into low-power mode, it needs to turn off its
clocks. Until now, the HSIC core driver has only turned off the clocks but
it did not call the clock uprepare API for decrementing the reference count
of these clocks. This allows saving extra power and TCXO shutdown. The fix
adds calls to the clock unprepare API on USB HSIC low-power mode entry and
calls to clock prepare API on USB HSIC low-power mode exit.

CRs-Fixed: 538872
Change-Id: I255d522e811dc5f94dd45168667cab8d782498d8
Signed-off-by: Danny Segal <dsegal@codeaurora.org>