Input: add Qualcomm PM8941 power key driver

Signed-off-by: Courtney Cavin <courtney.cavin@sonymobile.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Tested-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>