cmd/compile: add arm64 rules to optimize go codes to constant 0

Optimize the following codes to constant 0.

  function shift (x uint32) uint64 {
    return uint64(x) >> 32
  }

Change-Id: Ida6b39d713cc119ad5a2f01fd54bfd252cf2c975
Reviewed-on: https://go-review.googlesource.com/c/go/+/303830


Trust: fannie zhang <Fannie.Zhang@arm.com>
Run-TryBot: fannie zhang <Fannie.Zhang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>