Remove support for AMD's 3Dnow.

AMD stopped release new chips withe 3DNow in 2010.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
Refactoring and simplifying of CPU detection.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
libFLAC/stream_encoder.c : Reduce about of  hackery.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
Add AVX/AVX2/FMA support to CPU detection code.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
Add AVX2 CPU support stream encoder.

Patch-from: lvqcl <lvqcl.mail@gmail.com>