[RISCV] Rename suffixes on VCPOP/VMSBF/VMSET/etc pseudos. NFC (#119785)
These are suffixed with B1, B2, B4, B8, B16, B32, or B64 which I think
these were supposed to match the naming of the vbool types from C where
the number should be SEW/LMUL. So the smallest mask is 64 and the
largest is 1. This provides a compact syntax for describing the 7
possible ratios between LMUL and SEW.
We had the instruction names in the opposite order.