phy: omap-usb2: use *syscon* framework API to power on/off the PHY

Deprecate using phy-omap-control driver to power on/off the PHY,
and use *syscon* framework to do the same. This handles
powering on/off the PHY for the USB2 PHYs used in various TI SoCs.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>