drm/i915: Revert i915.semaphore=1 default from i915 merge

My Q67 / i7-2600 box has rev09 Sandy Bridge graphics.  It hangs
instantly when GNOME loads and it hangs so hard the reset button
doesn't work.  Setting i915.semaphore=0 fixes it.

Semaphores were disabled in a1656b90 ("drm/i915: Disable GPU
semaphores by default") in 2.6.38 but were then re-enabled (by mistake?)
by the merge 47ae63e0

 ("Merge branch 'drm-intel-fixes' into
drm-intel-next").

(It's worth noting that the offending change is i915_drv.c, which was
not marked as a conflict - although a 'git show --cc' on the merge does
show that neither parent had it set to 1)

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>