r600g: adjust flush flags (v3)

r600g: adjust flush flags (v3)

1. flush SH with read caches
2. add flag for DB flushes
3. add flag for CB flushes

v2: flush all CBs, remove redundant emit_state variable.
v3: Marek: also set the new flags in r600_context_flush, the CP dma functions,
    and texture_barrier, and rename them

Signed-off-by: Marek Olšák <maraeo@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>