Handle refresh rate as float in general, and add also extra
attributes (interlaced, doublescan) for video modes.
Make it possible to select exact mode (interlaced / doublescan modes
will not be selected), and allow close matches such as 49.5 Hz
for PAL 50 Hz.
Add a display server construct for DRM/KMS mode. The main use is
to provide resolution changes (including automatic refresh rate
switch) for this configuration, i.e. DRM context and OpenGL drivers.
To enable refresh rate restoration after automatic refresh rate
change, av_info->timing_fps is also adjusted on core close / RA exit.
No effects expected on CRTSwitchRes.
