The memmove implementation relies on the variable
runtime.arm64UseAlignedLoads to select fastest code
path. Considering Neoverse N3, V3 and V3ae cores
prefer aligned loads, this patch adds code to detect
them for memmove performance.

Change-Id: I7266fc35d8b2c15ff516c592b987bafacb82b620
Reviewed-on: https://go-review.googlesource.com/c/go/+/664038


Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>