Input: matrix_keypad - add support for clustered irq

This one adds support of a combined irq source for the whole matrix keypad.
This can be useful if all rows and columns of the keypad are e.g. connected
to a GPIO expander, which only has one interrupt line for all events on
every single GPIO.

Signed-off-by: Luotao Fu <l.fu@pengutronix.de>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>