Define vleff intrinsics and lower to V instructions.
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>
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D93516