[AArch64][LV] AArch64 does not prefer vectorized addressing

TTI::prefersVectorizedAddressing() try to vectorize the addresses that lead to loads.
For aarch64, only gather/scatter (supported by SVE) can deal with vectors of addresses.
This patch specializes the hook for AArch64, to return true only when we enable SVE.

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D124612