phy: meson: add USB2 PHY support for Meson8b and GXBB

This is a new driver for the USB PHY found in Meson8b and GXBB SoCs.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>