arm64: dts: r8a7795: salvator-x: Enable I2C for DVFS device

This patch enables I2C for DVFS device for for Salvator-X board on
R8A7795 SoC.

Signed-off-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>