Input: add driver for Broadcom keypad controller

Broadcom Keypad controller is used to interface a SoC with a matrix-type
keypad device. The keypad controller supports multiple row and column
lines. A key can be placed at each intersection of a unique row and a
unique column. The keypad controller can sense a key-press and key-release
and report the event using an interrupt to the CPU.

Reviewed-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>