linux-imx

media: dvb uAPI docs: document demux mmap/munmap syscalls

With the new dmx mmap interface, those two syscalls are now
handled by the subsystem. Document them.

This patch is based on the V4L2 text for those ioctls.

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