freedreno: we have more than 0 viewports!

4155d1c7 'st/mesa: drop dependence on API profile in st_init_extensions'
broke freedreno because somehow 'PIPE_CAP_MAX_VIEWPORTS' fell through
the cracks.  Resulting that we reported zero viewports.  So the state
tracker never bothered to give us any valid viewport!

Signed-off-by: Rob Clark <robclark@freedesktop.org>