radeonsi/gfx9: reduce max threads per block to 1024 on gfx9+

radeonsi/gfx9: reduce max threads per block to 1024 on gfx9+

The number of supported waves per thread group has been reduced to 16
with gfx9. Trying to use 32 waves causes hangs, and barriers might
not work correctly with > 16 waves.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
(cherry picked from commit a0e6b9a2db5aa5f06a4f60d270aca8344e7d8b3f)
[Emil Velikov: add a HAVE_LLVM check, as applicable in branch]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Conflicts:
	src/gallium/drivers/radeon/r600_pipe_common.c