drm/i915: rip out TV-out lore ...

This seems to be an impressive piece of copy&pasta lore. I've
checked all docs and on most platforms these bits are all MBZ, with
the exception of the SDVO pixel multiplier on gen3. On gen4 that
moved to a special DPLL_MD registers.

No indication whatsoever that we actually need this for native
TV-out support. I suspect this started as a hack when we didn't
yet have proper pixel multiplier support in place for SDVO TV, but
then got stuck in a life of its own.

Just rip it out.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>