i965: Add PIPE_CONTRTOL_DATA_CACHE flush to brw_emit_mi_flush().

Although we're phasing out brw_emit_mi_flush(), we still use it in some
places in order to "flush everything".  In a number of those places, we
write data to a buffer that we may then bind as an image surface, SSBO,
or atomic buffer.  Those usages require us to flush the data cache.

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

src/mesa/drivers/dri/i965/brw_pipe_control.c

@@ -449,6 +449,7 @@ brw_emit_mi_flush(struct brw_context *brw)
       if (devinfo->gen >= 6) {
          flags |= PIPE_CONTROL_INSTRUCTION_INVALIDATE |
                   PIPE_CONTROL_CONST_CACHE_INVALIDATE |
+                  PIPE_CONTROL_DATA_CACHE_FLUSH |
                   PIPE_CONTROL_DEPTH_CACHE_FLUSH |
                   PIPE_CONTROL_VF_CACHE_INVALIDATE |
                   PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE |