[ARM] pxa/spitz: add gpio button support (fixes regression)

Updating desc for lid keys and resending patch with proper comments:
Define Spitz buttons as GPIO keys in a way compatible with the old driver:

On/Off: As Suspend EV_PWR key
Raw values of lid sensors SWA and SWB: As EV_SW switches
SWA: Display Down
SWB: Lid Closed
Recommended user space decoding:
SWA==0 & SWB==0: lid opened (landscape mode)
SWA==1 & SWB==0: invalid (or mechanic race condition)
SWA==0 & SWB==1: lid closed with display up (portrait mode or mechanic
                 race condition while closing to display-less mode)
SWA==1 & SWB==1: lid closed with display down (display-less mode)

AK_INT remote trigger is not mapped as input event. Without complete
remote driver and remote pull-up control it has no useful
interpretation.

Signed-off-by: Stanislav Brabec <utx@penguin.cz>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>