Input: ADP5589 - new driver for I2C Keypad Decoder and I/O Expander

From http://www.analog.com/ADP5589

:
The ADP5589 is an I/O port expander and keypad matrix decoder designed
for QWERTY type phones that require a large keypad matrix and expanded
I/O lines.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>