When the internal/cpu package was introduced, the AES package still used
the custom crypto/internal/cipherhw package for amd64 and s390x. This
change removes that package entirely in favor of directly referencing the
cpu feature flags set and exposed by the internal/cpu package. In
addition, 5 new flags have been added to the internal/cpu s390x struct
for detecting various cipher message (KM) features.

Change-Id: I77cdd8bc1b04ab0e483b21bf1879b5801a4ba5f4
GitHub-Last-Rev: a611e3ecb1f480dcbfce3cb0c8c9e4058f56c1a4
GitHub-Pull-Request: golang/go#24766
Reviewed-on: https://go-review.googlesource.com/105695Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>