sh-pfc: r8a7790: Add I2C pin groups and functions

Adds pinmux for i2c bus 1 and 2. (Pins for 0 and 3 are not multiplexed.)

Signed-off-by: Ulrich Hecht <ulrich.hecht@gmail.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>