drm/vmwgfx: Add CAP2 support in vmwgfx

The device exposes a new capability register. Add support for it.

Signed-off-by: Neha Bhende <bhenden@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>