[dev.simd] simd: add arm64 Neon support to midway

Add Neon to Midway.

Change-Id: I05968666a547ec131c562980a9589ea35add4cf8
Reviewed-on: https://go-review.googlesource.com/c/go/+/781961
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Alexander Musman <alexander.musman@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>