[media] ati_remote: Add comments to keycode table

A more detailed description of what the buttons look like and
their intended function makes it easier for people to maintain
this code without access to the hardware.

[m.chehab@samsung.com: Fixed a typo "Mdeia" instead of "Media"]
Signed-off-by: George Spelvin <linux@horizon.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>