i2c: rcar: Add compatible support for r8a77990 (R-Car E3)

This patch adds compatible string support for the Renesas R-Car E3
(r8a77990) SoC.

Signed-off-by: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>