Workaround for some Radeon SI cards (Alex Deucher)
Fix 24p and 24.0 playback by calculating the modelines correctly (via https://bugs.freedesktop.org/show_bug.cgi?id=69675)
Calulate Modelines more accurately (via: https://bugs.freedesktop.org/show_bug.cgi?id=69675)
Merge pull request #2738 from fritsch/master

AMD: Modeline calculation and stability fixes