usb: dwc3: adapt dwc3 core to use Generic PHY Framework

Adapted dwc3 core to use the Generic PHY Framework. So for init, exit,
power_on and power_off the following APIs are used phy_init(), phy_exit(),
phy_power_on() and phy_power_off().

However using the old USB phy library wont be removed till the PHYs of all
other SoC's using dwc3 core is adapted to the Generic PHY Framework.

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