media: dt-bindings: i2c: Add I2C Address Translator (ATR)

Add bindings for I2C Address Translator. Only one property is added,
'i2c-alias-pool', which can be used in the bindings for the device that
supports ATR.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>