vmwgfx: Implement a proper GMR eviction mechanism

Use Ben's new range manager hooks to implement a manager for
GMRs that manages ids rather than ranges.
This means we can use the standard TTM code for binding, unbinding and
eviction.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>