usb: phy: qmp: Select usb3 phy mode before initializing PHY

Make sure the USB3/DP PHY mode selection is switched back to
USB3 mode before proceeding with PHY initialization. This fixes
a bug when DisplayPort previously uses the PHY and does not
switch it back which causes the POWER_DOWN_CONTROL register write
to not take effect and results in USB3 PHY initialization failure.

Change-Id: Idad0f80eda6192ccae9e824f1f76c7071806ffec
Signed-off-by: Jack Pham <jackp@codeaurora.org>