dt-bindings: reset: bitmain,bm1880-reset: Convert to yaml

Convert the device tree bindings for the Bitmain BM1880 reset controller
to YAML schema to allow participating in DT validation.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220407154338.4190674-4-p.zabel@pengutronix.de