[RISCV][NFC] Rename variables in rvv intrinsics related files.

This patch does the same thing as D125886 did.

- Use `Overloaded` rather than `Mangled`.
- Use `Prototype` or `Desc` rather than `Seq`, it's not just a string
sequence.

Reviewed By: fakepaper56

Differential Revision: https://reviews.llvm.org/D126634