ttm usage inconsistency

[Dave Airlie]

This is probably something I knew about and forgot, but I'll ask if
anyone has considered cleaning it up (or maybe I should fix nouveau).

nouveau sets up the resource manager using vram_size >> PAGE_SHIFT as
the bounds, but the bo sizes are in bytes, hence usage ends up being
accounted in bytes, so we have usage > size which looks wierd and also
caused me to screw up adding an ioctl for userspace.

Should I just make nouveau use vram_size instead?

Dave.