ARM: dts: lager: use demuxer for IIC3/I2C3

Create a separate bus for da9063 PMIC and da9210 regulator
related I2C slaves.

Based on similar work for HDMI by Wolfram Sang.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
[wsa: rebased, corrected chip name in commit msg, updated aliases]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>