drm/i915: Fix PTE decode during initial plane readout

When multiple pipes are enabled by the BIOS we try to read out each
in turn. But we do the readout for the second only after the inherited
vma for the first has been rebound into its original place (and thus
the PTEs have been rewritten). Unlike the BIOS we set some high caching
bits in the PTE on MTL which confuses the readout for the second plane.
Filter out the non-address bits from the PTE value appropriately to
fix this.

I suppose it might also be possible that the BIOS would already set
some caching bits as well, in which case we'd run into this same
issue already for the first plane.

TODO:
- should abstract the PTE decoding to avoid details leaking all over
- should probably do the readout for all the planes before
  we touch anything (including the PTEs) so that we truly read
  out the BIOS state
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Tested-by: Paz Zcharya <pazz@chromium.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240202224340.30647-8-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_plane_initial.c

@@ -72,7 +72,7 @@ initial_plane_vma(struct drm_i915_private *i915,
 			return NULL;
 		}
 
-		phys_base = pte & I915_GTT_PAGE_MASK;
+		phys_base = pte & GEN12_GGTT_PTE_ADDR_MASK;
 		mem = i915->mm.regions[INTEL_REGION_LMEM_0];
 
 		/*