[RISCV] Define vector single-width reduction intrinsic.

integer group:
vredsum/vredmaxu/vredmax/vredminu/vredmin/vredand/vredor/vredxor
float group:
vfredosum/vfredsum/vfredmax/vfredmin

We work with @rogfer01 from BSC to come out this patch.

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

Differential Revision: https://reviews.llvm.org/D93746