Input: add PS/2 serio driver for AVR32 devices

Add support for the PSIF peripheral on AVR32 AP7 devices.  It is implemented
as a serio driver and will behave like a serio 8042 device.

The driver has been tested with a Dell keyboard capable of running on 3.3
volts and a Logitech mouse on the STK1000 + STK1002 starter kit.  The Logitech
mouse was hacked by cutting the cord and using a bi-directional voltage
converter to get the required 5 volt I/O level.

For more information about the PSIF module, see the datasheet for AT32AP700X at
http://www.atmel.com/dyn/products/datasheets.asp?family_id=682

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