freedreno: Immediately compile a default variant of shaders.

freedreno: Immediately compile a default variant of shaders.

Now that we normalize our keys fairly well, build a variant at shader
state creation time so that hopefully you don't have to call the compiler
at draw time (as is now the case with glmark2 ES and most of the humus GL
demos).

Fixes: #2782
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4562>