This reverts commit 65f746e8.

As commit 8a473dba ("drm/i915: Fix DMA mapped scatterlist walks") and
commit 934941ed ("drm/i915: Fix DMA mapped scatterlist lookup") fixed
the DMA scatterlist limitations in the i915 driver, remove this temporary
workaround.

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Tom Murphy <murphyt7@tcd.ie>
Cc: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20201231005323.2178523-4-baolu.lu@linux.intel.comSigned-off-by: Will Deacon <will@kernel.org>