drm/i915/tv: Deobfuscate preferred mode selection

Rewrite the preferred mode selection to just check
whether the TV modes is HD or SD. For SD TV modes we
favor 480 line modes, for 720p we prefer 720 line modes,
and for 1080i/p we prefer 1080 line modes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181112170000.27531-10-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>