media: dt-bindings: media: i2c: max9286: Add support for per-port supplies

Power supplies for the ports can be controlled per port depending on the
hardware design. Support per-port supplies in the DT bindings, mutually
exclusive with the global supply.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>