phy: meson8b-usb2: add support for the USB PHY on Meson8 SoCs

Meson8 uses the same USB PHY as found on the Meson8b and GXBB SoCs. Add
a new of_device_id to indicate this. Also update the Kconfig option and
MODULE_DESCRIPTION accordingly.

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