Revert "drm/i915: GFX_MODE Flush TLB Invalidate Mode must be '1' for scanline waits"

Revert "drm/i915: GFX_MODE Flush TLB Invalidate Mode must be  '1' for scanline waits"

This reverts commit 393143615d9f2f581d87387268dc11b95adc339c, which
was commit f05bb0c7b624252a5e768287e340e8e45df96e42 upstream.

This has been found to cause GPU hangs when backported to 3.2, though
not in mainline.

References: http://bugs.launchpad.net/bugs/1140716
Cc: Steve Conklin <sconklin@canonical.com>
Cc: Stefan Bader <stefan.bader@canonical.com>
Cc: Bradd Figg <brad.figg@canonical.com>
Cc: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>