nv50,nvc0: use condition for occlusion queries when already complete

For the NO_WAIT variants, we would jump into the ALWAYS case for both
nested and inverted occlusion queries. However if the query had
previously completed, the application could reasonably expect that the
render condition would follow that result.

To resolve this, we remove the nesting distinction which unnecessarily
created an imbalance between the regular and inverted cases (since
there's no "zero" condition mode). We also use the proper comparison if
we know that the query has completed (which could happen as a result of
an earlier get_query_result call).

Fixes KHR-GL45.conditional_render_inverted.functional

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: 19.0 <mesa-stable@lists.freedesktop.org>
(cherry picked from commit e00799d3)