Use the NDK cpufeatures directly.

This brings the webp source closer to upstream and removes a very out of
date copy of the NDK's cpu-features.[ch] which upstream doesn't have.

(To avoid the need for exactly this copy & paste, the NDK's copy of the
cpufeatures library is built as part of the platform too.)

Bug: http://b/18556103
Change-Id: I82fb692c758d4855efa12ca7b743ce2893776a77
6 files changed