r600: add support for hw atomic counters. (v3)

r600: add support for hw atomic counters. (v3)

This adds support for the evergreen/cayman atomic counters.

These are implemented using GDS append/consume counters. The values
for each counter are loaded before drawing and saved after each draw
using special CP packets.

v2: move hw atomic assignment into driver.
v3: fix messing up caps (Gert Wollny), only store ranges in driver,
drop buffers.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Acked-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Tested-By: Gert Wollny <gw.fossdev@gmail.com>