[NFC][AArch64][LV] Reorganise tests for using SLEEF symbols in LV.

The tests introduced by https://reviews.llvm.org/D134719 and later
modified in https://reviews.llvm.org/D146839 are not testing LV in
isolation. This patch:
  1. Assures that all tests test LV in isolation.
  2. Adds LV tests using llvm intrinsics that have libm mappings.

llrint, llround and lrint are not included as currently
IR verifier pass does not allow to use vector types with them.

Author: JolantaJensen