dt-bindings: input: pm8941-pwrkey: Convert pm8941 power key binding to yaml

Convert qcom pm8941 power key binding from .txt to .yaml format.

The example has been removed in favour of full example being
available in the qcom,pon.yaml binding.

Signed-off-by: satya priya <skakit@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/1620800053-26405-5-git-send-email-skakit@codeaurora.org


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>