r600g: do all CUBE ALU operations before gradient texture operations (v2.1)

r600g: do all CUBE ALU operations before gradient texture operations (v2.1)

This moves all the CUBE section above the gradients section,
so that the gradient emission happens on one block which
is what sb/hardware expect.

v2: avoid changes to bytecode by using spare temps
v2.1: shame gcc, oh the shame. (uninit var warnings)

Cc: "10.4 10.3" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Glenn Kennard <glenn.kennard@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>