i965/tex: Don't create read-write textures with non-renderable formats
i965/tex: Don't create read-write textures with non-renderable formats

I haven't actually seen this bug in the wild, but it's possible that
someone could ask to do a S3TC PBO download or something.  This protects us
from accidentally creating a render target with a compressed or otherwise
non-renderable format.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler