usb: dwc3: msm: Perform phy_sleep_clk reset from HS PHY driver

The gcc_usb2{a,b}_phy_sleep_clk is better suited to be handled
by the USB HS PHY driver rather than by the SSUSB controller.
Thus, the HS PHY driver should be the one to call
clk_get()/prepare()/enable() on this clock.

Since it may also support asynchronous reset functionality,
introduce a usb_phy_reset() routine to the HS PHY driver, and let
the dwc3-msm driver call that instead of directly manipulating it.

Change-Id: I71355abcc3fbda56b4012b47f5e5e1624c36d4ea
Signed-off-by: Jack Pham <jackp@codeaurora.org>