r600: fix texture gradients instruction emission (v2)

r600: fix texture gradients instruction emission (v2)

The piglit tests were failing, and it appeared to be SB
optimising out things, but Glenn pointed out the gradients
are meant to be clause local, so we should emit the texture
instructions in the same clause. This moves things around
to always copy to a temp and then emit the texture clauses
for H/V.

v2: Glenn pointed out we could get another ALU fetch in
the wrong place, so load the src gpr earlier as well.

Fixes at least:
./bin/tex-miplevel-selection textureGrad 2D

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