input: matrix-keypad: Move to threaded irq handling

This change moves IRQ handling to threaded IRQ and
removes all instances of spinlock. This is needed for
those gpio IRQ's which are over slow bus (such as I2C)

Change-Id: I943df269c65296fff9f239830d56a625eb2fb71d
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>