ANDROID: input: keychord: Add keychord driver

This driver allows userspace to receive notification when client
specified key combinations are pressed.
The client opens /dev/keychord and writes a list of keychords
for the driver to monitor.
The client then reads or polls /dev/keychord for notifications.
A client specified ID for the keychord is returned from read()
when a keychord press is detected.

Signed-off-by: Mike Lockwood <lockwood@android.com>

keychord: fix to build without CONFIG_PREEMPT

Change-Id: I911f13aeda4224b6fa57863bc7e8972fec8837fb

[AmitP: Folded following android-4.9 commit changes into this patch
        f4d1cf1208fe ("ANDROID: input: misc: keychord: move header to uapi")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>