usb: phy: qusb: Add support to hold QUSB PHY into reset state

On some platform multiple QUSB PHYs instances are available and
based on platform variant those are used. If QUSB PHY is unused,
there is leakage current observed with that QUSB PHY related voltage
rail as QUSB PHY is out of reset on chip reset. This change adds
support to hold QUSB PHY into reset state if it is required.

Change-Id: I0ee7c42c1a3fb1298200f6348cc80aa621d57d88
Signed-off-by: Mayank Rana <mrana@codeaurora.org>