Input: add gpio-mouse driver

Adds support for simulating a mouse using GPIO lines. The driver
needs an appropriate platform device to be created by architecture
code.

The driver has been tested on AT32AP7000 microprocessor using the
ATSTK1000 development board.

Signed-off-by: Hans-Christian Egtvedt <hcegtvedt@atmel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>