[media] rc: gpio-ir-recv: add timeout on idle

Many decoders require a trailing space (period without IR illumination)
to be delivered before completing a decode.

Since the gpio-ir-recv driver only delivers events on gpio transitions,
a single IR symbol (caused by a quick touch on an IR remote) will not
be properly decoded without the use of a timer to flush the tail end
state of the IR receiver.

This patch initializes and uses a timer and the timeout field of rcdev
to complete the stream and allow decode.

The timeout can be overridden through the use of the LIRC_SET_REC_TIMEOUT
ioctl.

Signed-off-by: Eric Nelson <eric@nelint.com>
Acked-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>