dt-bindings: reset: st,sti-picophyreset: Convert to yaml

Convert the device tree bindings for the STMicroelectronics STi
SoftReset controller to YAML schema to allow participating in DT
validation.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220407154338.4190674-12-p.zabel@pengutronix.de