Add the Ooura FFT to RealFourier.

We are using the Ooura FFT in a few places:
- AGC
- Transient suppression
- Noise suppression

The optimized OpenMAX DL FFT is considerably faster, but currently does
not compile everywhere, notably on iOS. This change will allow us to use
Openmax when possible and otherwise fall back to Ooura.

(Unfortunately, noise suppression won't be able to take advantage of it
since it's not C++. Upgrade time?)

R=aluebs@webrtc.org, mgraczyk@chromium.org

Review URL: https://webrtc-codereview.appspot.com/45789004

Cr-Commit-Position: refs/heads/master@{#8798}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8798 4adac7df-926f-26a2-2b94-8c16560cd09d
20 files changed