arm64: dts: renesas: r8a77990: Add I2C-DVFS device node

This patch adds I2C-DVFS device node for the R8A77990 SoC.

v2
* Drop aliases update as in upstream it is not required to configure the
  BD9571 PMIC for DDR backup, nor is the use of i2c are aliases desired.
* Do not describe the device as compatible with "renesas,rcar-gen3-iic" or
  "renesas,rmobile-iic" fallback compat strings. The absence of automatic
  transmission registers leads us to declare the r8a77990 IIC controller as
  incompatible.

v2.1
* Reduced register range to reflect documentation

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>