[zlib] Add Android ARM aarch64 feature detection

Android aarch64 has different PMULL and CRC32 feature values compared
to Android aarch32.

Rename init_arm_features to _arm_check_features to be consistent with
the _MSC_VER code. Add Android aarch64 feature value support. Use the
correct return type for the platform feature detectors (getauxval and
android_getCpuFeatures). Add comments and a TODO for OS_ZIRCON.

Bug: 810125
Change-Id: Ie1526b1d6d3ebeba76d49a83911b335ffce1b288
Reviewed-on: https://chromium-review.googlesource.com/c/1472810


Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#632710}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f0a643baf4ad71b81063fce307db839e2d9ba88f