xhci-plat: Add hibernation support to xhci platform

Add hibernation support to xhci platform by adding
the proper PM ops freeze and restore.
Also set the hibernated argument to xhci_resume which
will trigger the reset-resume of the connected
root-hubs and the devices.

Change-Id: Ib536bb2485928326f34bfc3422b672cc62309efe
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>