Input: add Atmel AT42QT1070 keypad driver

The AT42QT1070 QTouch sensor supports up to 7 keys.

The driver has been tested on Atmel AT91SAM9M10-G45-EK board, and it
 should work fine on other platforms.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>