MIPS optimizations for ISAC (patch #3)

Implemented functions:
- WebRtcIsacfix_MatrixProduct1
- WebRtcIsacfix_MatrixProduct2

The optimizations are bit-exact to the C code.

R=andrew@webrtc.org, tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/18019004

Patch from Ljubomir Papuga <lpapuga@mips.com>.

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6919 4adac7df-926f-26a2-2b94-8c16560cd09d