Add compatible string for V3s, with H3 one as fallback.

This is used in device tree now, but not standardized in DT binding.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201003235018.1121618-2-icenowy@aosc.ioSigned-off-by: Arnd Bergmann <arnd@arndb.de>