dt-bindings: clock: renesas: rcar-usb2-clock-sel: Add support for RZ/G2 M/N/H

dt-bindings: clock: renesas: rcar-usb2-clock-sel: Add support for RZ/G2 M/N/H

The datasheet for the RZ/G2 Series show the bit for choosing between a crystal
oscillator and an external oscillator is present.  Add the bindings for
r8a774a1 (RZ/G2M), r8a774b1 (RZ/G2N), and r8a774e1 (RZ/G2H)

Signed-off-by: Adam Ford <aford173@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201228202221.2327468-1-aford173@gmail.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>