[RISCV] Adjust RISCVInstrInfoVSDPatterns.td for different pseudo instructions for different FPR.

Move the Suffix string into the VTypeInfo class so we don't need a helper class to get to it.

Adjust pseudo naming scheme for FPRs to put F16/F32/F64 in
place of F in the pseudo instruction name rather than as a suffix.
This avoids special cases like VFMERGE from the original patch.

Differential Revision: https://reviews.llvm.org/D95404