phy: amlogic: add Amlogic G12A USB2 PHY Driver

This adds support for the USB2 PHY found in the Amlogic G12A SoC Family.

It supports Host and/or Peripheral mode, depending on it's position.
The first PHY is only used as Host, but the second supports Dual modes
defined by the USB Control Glue HW in front of the USB Controllers.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>