drm/i915: remove render reclock support

This code generally fails to adjust the render clock, and when it does,
it conflicts with some other register settings and can cause problems.

So remove this code altogether.  I'm reworking it now to do the right
thing, but the only bit it will share is the VBT check for whether
reclocking is supported, so I'm leaving that bit.

Reverts most of 652c393a ("add dynamic
clock frequency control"), though for many the regressions showed up
in the later 181a5336 ("Fix render
reclock availability detection").

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>