CPU feature detection

Initially added CPU feature detection in winpr/sysinfo.
The detection provides the following two functions through the winpr API to check if a feature is supported:
IsProcessorFeaturePresent
IsProcessorFeaturePresentEx
For a list of available flags have a look into winpr/sysinfo.h but not all are implemented yet.

The detection currently works on
- on i386/amd64 on any platform when compiling with gcc
- ARM on linux (Android)
- (window - but not tested)

All detection is now done in a single place - primitives and rfx-codec where adapted to use the new API instead of using their own code. For rfx the detection is done in the decoder during initialization. This way the client doesn't need to take care of any detection - updated xfreerdp accordingly.