dt-bindings: watchdog: qcom,pm8916-wdt: convert to dtschema

Convert the Qualcomm PM8916 watchdog timer controller bindings to DT
schema and include them in parent device schema.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220726120215.101868-3-krzysztof.kozlowski@linaro.org