drm/i915: limit PPGTT size to 2GB in 32-bit platforms

We already set this limit for the GGTT.

This is a temporary patch until a full replacement of size_t variables
(inadequate in 32-bit kernel) is in place.

Regression from:
	commit a4e0bedc
	Author: Michel Thierry <michel.thierry@intel.com>
	Date:   Wed Apr 8 12:13:35 2015 +0100

		drm/i915: Use complete address space in true PPGTT

v2: Prettify code and explain why this is needed. (Chris)
v3: Don't hide the compilation warning in 32-bit. (Chris)
Suggested-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NMichel Thierry <michel.thierry@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -952,6 +952,13 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 
 	ppgtt->base.start = 0;
 	ppgtt->base.total = 1ULL << 32;
+	if (IS_ENABLED(CONFIG_X86_32))
+		/* While we have a proliferation of size_t variables
+		 * we cannot represent the full ppgtt size on 32bit,
+		 * so limit it to the same size as the GGTT (currently
+		 * 2GiB).
+		 */
+		ppgtt->base.total = to_i915(ppgtt->base.dev)->gtt.base.total;
 	ppgtt->base.cleanup = gen8_ppgtt_cleanup;
 	ppgtt->base.allocate_va_range = gen8_alloc_va_range;
 	ppgtt->base.insert_entries = gen8_ppgtt_insert_entries;