drm/vmwgfx: Add a parameter to get the max fb size

This can be used by the X server to restrict mode resolutions and size of
root pixmap.

Bump minor to announce this availability.
Bump driver date.

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