dt-bindings: reset: ath79: Convert to yaml

Convert the device tree bindings for the Qualcomm Atheros AR7xxx/AR9XXX
reset controller to YAML schema to allow participating in DT validation.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Alban Bedel <albeu@free.fr>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220407154338.4190674-2-p.zabel@pengutronix.de