freedreno/ir3: handle color clamp variant ourselves

freedreno/ir3: handle color clamp variant ourselves

Now that there is a pass to do this in NIR, lets just use that and
manage the variants ourself, rather than letting state-tracker do it.
This way, mesa/st will precompile shaders without requiring
ST_DEBUG=precompile (which requires a debug build).

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