Revert "drm/i915/bdw: Limit GTT to 2GB"

This reverts commit 3a2ffb65eec6dbda2fd8151894f51c18b42c8d41.

Now that the code is fixed to use smaller allocations, it should be safe
to let the full GGTT be used on BDW.

The testcase for this is anything which uses more than half of the GTT,
thus eclipsing the old limit.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_gem_gtt.c
Simple merge