This extends fetch_payload_reg() to support fetching vector registers like barycentrics stored on the payload as a contiguous sequence of SIMD-wide vectors. In the SIMD32 case, both halves of the SIMD16 vector registers specified as regs[0] and regs[1] are zipped to construct a single SIMD32-wide vector. Reviewed-by: Caio Oliveira <caio.oliveira@intel.com> Reviewed-by: Jordan Justen <jordan.l.justen@intel.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26606>