Revert "drm/i915: Disable SSC for outputs other than LVDS or DP"

Revert "drm/i915: Disable SSC for outputs other than LVDS or DP"

This reverts commit 633f2ea26665d37bb3c8ae30799aa14988622653 and the
attempted fix dcbe6f2b3d136995915e2f9ecc7d4f3b28f47b6c.

There is a single clock source used for both SSC (some LVDS and DP) and
non-SSC (VGA, DVI) outputs. So we need to be careful to only enable SSC
as necessary. However, fiddling with DREFCLK was causing DP links to be
dropped and we do not have a fix ready, so revert.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>