Revert "drm/i915: Enable PSR by default."

This reverts commit b6d54779.

The panel self refresh clearly isn't stable yet, and causes my laptop
(Haswell ULT in a Sony Vaio Pro) to have the screen lock up.  Maybe it
doesn't ever get out of self-refresh, or maybe there are gremlins in the
machine that get unhappy.  Regardless, it's broken, and it gets
reverted.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>