clk: qcom: Add support for gcc_usb2 ref clocks

For USB2 controller operation, there is requirement to add usb2 ref
clocks from gcc clock driver. Add support for the same by adding new
ref clocks.

Change-Id: Ie52f06c0f536cfe22df28c78f74f5034634aa335
Signed-off-by: Amit Nischal <anischal@codeaurora.org>