Input: sirfsoc_pwrc - add onkey input driver for CSR SiRFprimaII PWRC

Input: sirfsoc_pwrc - add onkey input driver for CSR SiRFprimaII PWRC

There is an embedded PWRC(power controller) in SiRFprimaII and SiRFatlasVI,
we have an ONKEY button which can generate interrupt to IRQ controller.
In a typical user scenarios, at the runtime, if users touch the key, we put
system to s2ram status.

Signed-off-by: Binghua Duan <Binghua.Duan@csr.com>
Signed-off-by: Xianglong Du <Xianglong.Du@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>