download of firmware halts/cancels build process

[seichter]

It seems that the XBox site was redesigned. The download for the firmware doesnt work and therefore halts the build process. Unless really needed this part should be configurable in the CMake build system as an option.

[piedar]

Thanks to #372, the BUILD_AUDIO flag has gone away. The BUILD_REDIST_PACKAGE=OFF flag makes the build invoke fwfetcher.py.

The download works for me, though it does take a full minute and a half despite 20 MB/s down.