Input: add new driver for ARM CLPS711X keypad

This patch adds a new driver for keypad for Cirrus Logic CLPS711X CPUs.
Target CPU contain keyboard interface which can scan 8 column lines,
so we can read row GPIOs to read status and determine asserted state.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>