Revert "drm/i915: Don't use BAR mappings for ring buffers with LLC"

This reverts commit 4eb6789f which is
commit 85636167 upstream.

It has been reported to cause problems on Alpine Linux and Manjaro Linux
5.15-based releases, so revert it for now until it can be sorted out.

Reported-by: "A.P. Jo." <apjo@tuta.io>
Link: https://lore.kernel.org/r/NQJqG8n--3-9@tuta.io
Link: https://gitlab.alpinelinux.org/alpine/aports/-/issues/14704


Reported-by: Philip Müller <philm@manjaro.org>
Link: https://lore.kernel.org/r/d955327b-cb1c-4646-76b9-b0499c0c64c6@manjaro.org
Link: https://gitlab.freedesktop.org/drm/intel/-/issues/8284


Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.9+
Cc: Jouni Högander <jouni.hogander@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>