arm64: dts: renesas: r8a77990: ebisu: Add I2C EEPROM for PMIC

Add a device node for the I2C EEPROM which serves as external storage
for the PMIC setup, as a backup of the internal OTP configuration.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/32443cd203ce2787d9a719d06a473b9e9cd508c2.1625489160.git.geert+renesas@glider.be