dt-bindings: trivial-devices: Add silabs,em3581

Add Silicon Labs EM3581 Zigbee SoC to trivial-devices.

Signed-off-by: Vincent Tremblay <vincent@vtremblay.dev>
Link: https://lore.kernel.org/r/20221227023550.569547-1-vincent@vtremblay.dev


Signed-off-by: Mark Brown <broonie@kernel.org>