usb: phy: qmp: Add support for SS_PHY LDO clock

The SS_PHY_LDO is a signal that controls the buffer that
receiving the external reference clock. This signal is
provided by the clock driver and should be enabled once
by the QMP PHY driver upon bootup.

Change-Id: Ibe1b7a8f6d8830e113a2f1ce69abe330bc0d417b
Signed-off-by: Jack Pham <jackp@codeaurora.org>