The patch is a replacement of D125199. PseudoReadVL with vtype has worry for
computing same vtypes of VLEFF/VLSEGFF in two different places, DAGToDAG and
InsertVSETVLI. VLEFF/VLSEGFF MI with VL output still could provide the vtype of
VLEFF/VLSEGFF to the users of its VL.
The patch names the new pseudo as original VLEFF/VLSEGFF name suffixed "_VL" and
expand them in RISCVInsertVSETVLI pass.
This patch also reverts commit 4537aae0d57e17c217c192d8977012ba475b130c,
"[RISCV] Make PseudoReadVL have the vtypes of the corresponding VLEFF/VLSEGFF.".
Not sure how much value we have here from having the generic bit field for this over a static method which switches on the opcodes. This really only applies to the FF variants.