This reverts commit b12d691e.

It turns out this is not ready for primetime yet.  The intentions are
good, but using remap_pfn_range() requires that there is nothing already
mapped in the area, and the i915 code seems to very much intentionally
remap the same area multiple times.

That will then just trigger the

                BUG_ON(!pte_none(*pte));

in mm/memory.c: remap_pte_range().

There are also reports of mapping type inconsistencies, resulting in
warnings and in screen corruption.

Link: https://lore.kernel.org/lkml/20210519024322.GA29704@xsang-OptiPlex-9020/
Link: https://lore.kernel.org/lkml/YKUjvoaKKggAmpIR@sf/
Link: https://lore.kernel.org/lkml/b6b61cf0-5874-f4c0-1fcc-4b3848451c31@redhat.com/Reported-by: kernel test robot <oliver.sang@intel.com>
Reported-by: Kalle Valo <kvalo@codeaurora.org>
Reported-by: Hans de Goede <hdegoede@redhat.com>
Reported-by: Sergei Trofimovich <slyfox@gentoo.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>