phy: meson: add Amlogic G12A USB2 and USB3+PCIE PHY drivers

This adds support for the USB PHYs found in the Amlogic G12A SoC Family.

The USB2 PHY 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.

The second driver supports USB3 Host mode or PCIE 2.0 mode, depending on
the layout of the board.
Selection is done by the #phy-cells, making the mode static and exclusive.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>