input/tc3589x: add tc3589x keypad support

Add support for the keypad controller module found on the
TC3589X devices. This driver default adds the support for
TC35893 device.

Signed-off-by: Sundar Iyer <sundar.iyer@stericsson.com>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
[Some minor fixups for compilation]
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>