arm64: dts: renesas: r8a77990: Enable I2C DMA

This patch enables I2C DMA.

NOTE: I2C7 DMA is not supported by R-Car Gen3 Hardware User's Manual
Rev.0.80E.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Tested-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>