ARM: shmobile: koelsch: Remove duplicate i2c6 nodes

A second i2c6 node was a added by
05e234a187058ee ("ARM: shmobile: koelsch dts: Add VDD MPU regulator for
DVFS"). Merge this into the existing node.

Also shuffle i2c nodes so they are all together.

Cc: Gaku Inami <gaku.inami.xw@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>