i2c: sh_mobile: Add support for r8a774c0 (RZ/G2E)

Similarly to R-Car E3, RZ/G2E doesn't come with automatic
transmission registers, as such it is not considered compatible
with the existing fallback bindings.

Add SoC specific binding compatibility to allow for later
support for automatic transmission.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>