vmwgfx: Remove the possibility to map the fifo from user-space

This was previously used by user-space to check whether a fence
sequence had passed or not.
With fence objects that's not needed anymore.

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