dt-bindings: i2c: renesas,riic: Move ref for i2c-controller.yaml to the end

dt-bindings: i2c: renesas,riic: Move ref for i2c-controller.yaml to the end

In preparation for adding more validation checks, move the `$ref` for
'i2c-controller.yaml' to the end of the file. Also, relocate the
conditional check for 'resets' into the 'allOf' block.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250625104526.101004-2-prabhakar.mahadev-lad.rj@bp.renesas.com