ARM: dts: lager: rename and reindex i2cexio

The rename from i2cexio to i2cexio0 is in preparation for adding
i2cexio1 which will use the demuxer for IIC1/I2C1.

The reindexing from i2c8 to i2c10 is to allow space for grouping of
additional GPIO buses to be added by follow-up patches to support demuxing
of other i2c buses.

Also note that fallback to GPIO is not provided by the hardware for IIC0/I2C0.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
[wsa: rebased, fixed alias and removed typo in commit message]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>