Input: add driver for Sharp gp2ap002a00f proximity sensor

This driver adds support for Sharp's GP2AP002A00F proximity sensor. The
proximity is measured as a binary switch, i.e. an object is either
detected or not detected. Hence, this driver is implemented as a switch
that reports SW_FRONT_PROXIMITY.

Reviewed-by: Datta Shubhrajyoti <shubhrajyoti@ti.com>
Signed-off-by: Courtney Cavin <courtney.cavin@sonyericsson.com>
Signed-off-by: Oskar Andero <oskar.andero@sonyericsson.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>