[aarch64] Backport missing NEON intrinsics to GCC8

[Pop, Sebastian via Gcc-patches]

Hi,

gcc-8 branch is missing NEON intrinsics for loads and stores.
Attached patches pass bootstrap and regression testing on Graviton2 
aarch64-linux.

Ok to commit to gcc-8 branch?

Thanks,
Sebastian

0001-Patch-implementing-vld1_-_x3-vst1_-_x2-and-vst1_-_x3.patch
Description: 0001-Patch-implementing-vld1_-_x3-vst1_-_x2-and-vst1_-_x3.patch

0002-add-intrinsics-for-vld1-q-_x4-and-vst1-q-_x4.patch
Description: 0002-add-intrinsics-for-vld1-q-_x4-and-vst1-q-_x4.patch