Hardcode the ad hoc EDID parser to always claim that only SDR is
supported. Even though libdisplay-info is not yet asked for HDR
capabilities, it shall be the only way to see them.
To be nicer to experimenters, main.c adds a note that you really need
libdisplay-info if you want to play with HDR.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>