[VE] Isel patterns for fp32/64 and i32/64 conversion

Summary:
fp32/64 <> signed/unsigned i32/64 conversion isel patterns and tests

(This patch depends on `fsub` implemented by https://reviews.llvm.org/D73540 )

Reviewers: arsenm, craig.topper, rengolin, k-ishizaka

Reviewed By: arsenm

Subscribers: merge_guards_bot, wdng, hiraditya, llvm-commits

Tags: #ve, #llvm

Differential Revision: https://reviews.llvm.org/D73544