Input: pm8941-pwrkey - abstract register offsets and event code

In order to support resin thru the pwrkey driver (they are very
similar in nature) we need to abstract the handling in this driver.

First we abstract pull_up_bit and status_bit along in driver data.
The event code sent for key events is quiried from DT.

Since the device can be child of pon lookup regmap and reg from
parent if lookup fails (we are child).

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>