Formalized Real 16-bit FFT for APM.
It also prepares for introducing Real 16-bit FFT Neon code from Openmax to SPL. CL https://webrtc-codereview.appspot.com/1819004/ takes care of that, but this CL is a prerequisite of that one.
Tested audioproc with an offline file. Bit exact.

R=andrew@webrtc.org, rtoy@google.com

Review URL: https://webrtc-codereview.appspot.com/1830004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4390 4adac7df-926f-26a2-2b94-8c16560cd09d
10 files changed