dri: Allow selective generation of accum. buffer configs

dri: Allow selective generation of accum. buffer configs

Modify the interface to driCreateConfigs allowing drivers to not
expose configs with an accumuation buffer.  All of the drivers calling
function have been updated to pass true for the accumulation
selector.  This maintains the current behavior.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Corbin Simpson <MostAwesomeDude@gmail.com>