media: i2c: adv748x: Add support for i2c_new_secondary_device

The ADV748x has twelve 256-byte maps that can be accessed via the main
I2C ports. Each map has it own I2C address and acts as a standard slave
device on the I2C bus.

Allow a device tree node to override the default addresses so that
address conflicts with other devices on the same bus may be resolved at
the board description level.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>