[media] doc-rst: document LIRC set mode ioctls

Add LIRC_SET_[REC|SEND]_MODE ioctls to the corresponding
GET functions, and put all LIRC modes altogether.

As now everything is already documented on its own ioctl
pages, get rid of lirc_ioctl.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>