[AArch64] Increase scatter overhead on Neoverse-V2 (#101296)
This patch increases scatter overhead on Neoverse-V2 to 13. This
benefits s128 kernel from TSVC_2 test suite.
SPEC 17, RAJAPerf, and Sptter are unaffected by this patch.
This patch boosts s128 kernel's performance from TSVC test suite by about
40% as this enables vectorization. Also, handle minor code refactoring
for gather related part.