dt-bindings: i3c: mipi-hci: Include the bus binding

Update a little bit the content to match the bus binding, including:
- the node title should have been named after the description done
  in the historical i3c.txt file, ie: i3c-master@<address>
- child nodes should be accepted even though the drivers do not currently
  support it
- #address-cells and #size-cells are also mandatory and have specific
  values

Cc: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210121101808.14654-3-miquel.raynal@bootlin.com