media: rc: pwm-ir-tx: add new driver

This is new driver which uses pwm, so it is more power-efficient
than the bit banging gpio-ir-tx driver.

Signed-off-by: Sean Young <sean@mess.org>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Tested-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>