[RISCV][Clang] Add some RVV Floating-Point intrinsic functions.

Support vfclass, vfmerge, vfrec7, vfrsqrt7, vfsqrt instructions.

Reviewed By: craig.topper

Authored-by: Roger Ferrer Ibanez <rofirrim@gmail.com>
Co-Authored-by: Zakk Chen <zakk.chen@sifive.com>

Differential Revision: https://reviews.llvm.org/D99741