phy: da8xx-usb: new driver for DA8xx SoC USB PHY

This is a new phy driver for the SoC USB controllers on the TI DA8xx
family of microcontrollers. The USB 1.1 PHY is just a simple on/off.
The USB 2.0 PHY also allows overriding the VBUS and ID pins.

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