media: rc: remove ir-rx51 in favour of generic pwm-ir-tx

The ir-rx51 is a pwm-based TX driver specific to the N900. This can be
handled entirely by the generic pwm-ir-tx driver, and in fact the
pwm-ir-tx driver has been compatible with ir-rx51 from the start.

Note that the suspend code in the ir-rx51 driver is unnecessary, since
during transmit, the process is not in interruptable sleep. The process
is not put to sleep until the transmit completes.

Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Tested-by: Sicelo A. Mhlongo <absicsz@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>