Input: add driver for Atmel integrated touchscreen controller

The AT91SAM9RL SoC integrates a Touchscreen Controller which
can trigger ADC conversion periodically.

Signed-off-by: Justin Waters <justin.waters@timesys.com>
Signed-off-by: Dan Liang <dan.liang@atmel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>