dt-bindings: watchdog: Add Qualcomm PM8916 watchdog

Document support for the Watchdog Timer (WDT) Controller in the
Qualcomm PM8916 PMIC module.

LKML: https://patchwork.kernel.org/patch/10695223/



Signed-off-by: Loic Poulain <loic.poulain@linaro.org>