arm64: dts: renesas: r8a774c0: Add generic compatible string to IIC node

According to the Hardware User's Manual, automatic transmission for PMIC
control (DVFS) is not available" on the RZ/G2E SoC.  This really means
that support for automatic DVFS is not present, while the IIC automatic
transmission feature itself is still available, albeit not super useful.

Hence there is no longer a reason not to declare compatibility with the
R-Car Gen3-specific and generic versions.  Accordingly, extend the reg
property to cover the automatic transmission registers.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/d222c2faa63f95d672efa07e55e8d01bddd17e65.1624013699.git.geert+renesas@glider.be