shader_arb_add_src_param handled DW and TXP undid it again. Remove DZ DW from
the modifiers and handle it in the instruction. DZ cannot be handled by TXP as
is, so move the .z component to .w and make it DW-like. Using SZW+TXP is
likely more efficient than the RCP, MUL, TEX we'd get if we let
shader_arb_add_src_param do the job.