radeonsi: don't create an infinite number of variants

radeonsi: don't create an infinite number of variants

If a shader has code like this:

   uniform float timestamp;
   ...
   if (timestamp > 0.0)
      do_something()

And timestamp is modified each frame, we'll end up generating a new
variant per frame.

This commit introduces a hard limit on the number of variants we generate
for a single shader.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5121
Fixes: b7501184b90 ("radeonsi: implement inlinable uniforms")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12138>