i965/gen6+: Invalidate constant cache on brw_emit_mi_flush().
i965/gen6+: Invalidate constant cache on brw_emit_mi_flush().

In order to make sure that the constant cache is coherent with
previous rendering when we start using it for pull constant loads.

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler