dt-bindings: leds: Convert leds-lm3692x to YAML format

dt-bindings: leds: Convert leds-lm3692x to YAML format

Additional changes:

 - Add ref to common.yaml for child node.
 - Add I2C node at example.

Fix below warning:
  arch/arm64/boot/dts/freescale/imx8mq-librem5-r2.dtb: /soc@0/bus@30800000/i2c@30a40000/backlight@36:
	failed to match any schema with compatible: ['ti,lm36922']

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240821222001.591111-1-Frank.Li@nxp.com
Signed-off-by: Lee Jones <lee@kernel.org>