r600: implement callstack workaround for evergreen.

r600: implement callstack workaround for evergreen.

This is ported from the sb backend, there are some issues with
evergreen stacks on the boundary between entries and ALU_PUSH_BEFORE
instructions.

Whenever we are going to use a push before, we check the stack
usage and if we have to use the workaround, then we switch to
a separate push.

I noticed this problem dealing with some of the soft fp64 shaders,
in nosb mode, they are quite stack happy.

This fixes all the glitches and inconsistencies I've seen with them

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Tested-by: Elie Tournier <elie.tournier@collabora.com>
Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>