power: reset: qcom-pon: add support for pm8941-pon

For PM8941 we don't have a defined field to store the reset reason.
Support wrapping pwrkey and resin, but without writing the reset
reason.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>