usb: xhci-msm-hsic: Add support to disable HW clock gating

It is observed that HW clock gating is causing instability
in normal operation of xhci controller. Provide a DT
parameter that can be used to disabled clock gating in
hardware.

Change-Id: I5b413605ad002d7992094941958f516d5e302146
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>