r600g/sb: improve alu packing on cayman

r600g/sb: improve alu packing on cayman

Scheduler/register allocator in r600-sb was developed and optimized
on evergreen (VLIW-5) hardware, so currently it's not optimal for
VLIW-4 chips.
This patch should improve performance on cayman gpus due to better alu
packing, but also it tends to increase register usage, so overall positive
effect on performance has to be proven by real benchmarks yet.

Some results with bfgminer kernel on cayman:
source bytecode:       60 gprs, 3905 alu groups,
sbcl before the patch: 45 gprs, 4088 alu groups,
sbcl with this patch:  55 gprs, 3474 alu groups.

Signed-off-by: Vadim Girlin <vadimgirlin@gmail.com>