i965: get the proper vertex surface type for doubles on gen8+
i965: get the proper vertex surface type for doubles on gen8+

This commit adds support for PASSTHRU format when pushing
double-precision attributes.

Check glarray->Doubles in order to know if we should choose a format
that does a conversion to float, or just passthru the 64-bit double.

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler