Changed FFTW warning from AVX to no SSE

Changed FFTW warning from AVX to no SSE

Changed the cmake FFTW SIMD check warning from complaining about
AVX to complaining about missing SSE or SSE2.
With FFTW 3.3.4 the performance of FFTW with both SSE and AVX enabled
is often a bit better and never much worse than SSE along. Newer
Intel processors probably also perform better with AVX with FFTW 3.3.3
so we should not complain about the combination of SSE(2) and AVX,
but only when SSE is missing.

Change-Id: I3665a35ec98616f015d05e314c8fbb80a8862092