arm64: dts: mt8173-elm: Switch to SMC watchdog

Switch to SMC watchdog because we need direct control of HW watchdog
registers from kernel. The corresponding firmware was uploaded in
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3405

.

Signed-off-by: Pin-yen Lin <treapking@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220729053254.220585-1-treapking@chromium.org


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>