i965/fs: Generalize is_uniform() to is_periodic().
i965/fs: Generalize is_uniform() to is_periodic().

This will be useful in the SIMD lowering pass.

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler