aco: fix derivatives/intrinsics with SGPR sources

ds_swizzle_b32 requires a VGPR and DPP can't encode SGPR sources.

Fixes
dEQP-VK.graphicsfuzz.cov-derivative-uniform-vector-global-loop-count.

Cc: 21.1 mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10840>