drm/i915/tv: Rip out pipe-disabling nonsense from ->mode_set
drm/i915/tv: Rip out pipe-disabling nonsense from ->mode_set

The pipe and plane _are_ disabled when we call this. So replace it
all with the corresponding assert (as self-documenting code) and
rip out all the lore.

Checking for a disabled plane would require us to export those macros
from intel_display.c, but if the pipe is off the plane isn't working
either. So this single check is good enough.

Reviewed-by: Imre Deak <fbd5edba1988036c8923f0cca0cce6ac4811db29@intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs