dt-bindings: power: reset: qcom-pon: define pm8941-pon

On PM8941 pon doesn't store the reset reason. However we still need the
wrapping node for pwrkey and resin nodes. Add bindings for pm8941-pon
device.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>