Revert "drm/i915: Introduce private PAT management"

This reverts commit 4395890a.

It's been over a year since this was merged, and the actual users of
intel_ppat_get / intel_ppat_put never materialized.

Time to remove it!

v2: Unbreak suspend (Chris)
v3: Rebase, drop fixes tag to avoid confusion

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190702113149.21200-1-michal.winiarski@intel.com