input: Add Qualcomm pm8xxx keypad controller driver

Add Qualcomm PMIC8XXX based keypad controller driver
supporting upto 18x8 matrix configuration.

Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>