drm/i915: set num_fence_regs to 0 if there is no aperture

We can't fence anything without aperture.
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Stuart Summers <stuart.summers@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@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/20191029095856.25431-3-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_gem_fence_reg.c

@@ -846,7 +846,9 @@ void i915_ggtt_init_fences(struct i915_ggtt *ggtt)
 
 	detect_bit_6_swizzle(ggtt);
 
-	if (INTEL_GEN(i915) >= 7 &&
+	if (!i915_ggtt_has_aperture(ggtt))
+		num_fences = 0;
+	else if (INTEL_GEN(i915) >= 7 &&
 		 !(IS_VALLEYVIEW(i915) || IS_CHERRYVIEW(i915)))
 		num_fences = 32;
 	else if (INTEL_GEN(i915) >= 4 ||