Convert ziirave-wdt.txt to yaml format.

Additional change:
- Add i2c node in example.
- Add ref to watchdog.yaml

Fix below warning:
arch/arm64/boot/dts/freescale/imx8mq-zii-ultra-rmb3.dtb: /soc@0/bus@30800000/i2c@30a40000/watchdog@38:
	failed to match any schema with compatible: ['zii,rave-wdt']
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20240814161250.4017427-1-Frank.Li@nxp.comSigned-off-by: Rob Herring (Arm) <robh@kernel.org>