[Clang][AArch64] Capturing proper pointer alignment for Neon vld1 intrinsicts

Summary:
During CodeGen for AArch64 Neon intrinsics, Clang was incorrectly
assuming all the pointers from which loads were being generated for vld1
intrinsics were aligned according to the intrinsics result type, causing
alignment faults on the code generated by the backend.

This patch updates vld1 intrinsics' CodeGen to properly capture the
correct load alignment based on the type of the pointer provided as
input for the intrinsic.

Reviewers: t.p.northover, ostannard, pcc, efriedma

Reviewed By: ostannard, efriedma

Subscribers: echristo, plotfi, nickdesaulniers, efriedma, kristof.beyls, danielkiss, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79721