arm64: dts: renesas: r8a77990: ebisu: Add GPIO expander

Describe the ON Semiconductor PCA9654 I/O expander on the first I2C
bus, which provides 8 extra GPIOs.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>