[Intel-gfx] Checking the amount of memory pinned by i915_gem_object_get_pages_gtt()

[Vovo Yang]

Is there a way to check the amount of memory pinned by
i915_gem_object_get_pages_gtt(), it would be very helpful to check
system memory usage.

I think the pinned field in i915_gem_gtt has a different meaning and
doesn't indicate whether a gem object is pinned by
i915_gem_object_get_pages_gtt().

# cat /sys/kernel/debug/dri/0/i915_gem_gtt
   ffff9fe1e9a7a3c0:   X       4224KiB 3e 02  uncached dirty (pinned x
0) (ppgtt offset: 00c00000, size: 00420000, pages: 4K)