ARM: dts: rskrza1: Add I2C support

Enable the I2C bus, and add the following devices:
  - Two CAT9554 port expanders (8 GPIOs, interrupt not wired by
    default),
  - R1EX24016ASAS0A EEPROM.

The bus also contains a MAX9856 Audio Codec, which is not yet supported.

All devices (incl. the audio codec) are documented to support an I2C bus
running at 400 kHz.

Pinctrl is based on the RZ/A BSP.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>