squeezelite: restructure package variants

squeezelite: restructure package variants

The squeezelite packages were lacking some features/codecs
(ssl, opus, wma, dsd and resampling) and required manual compilation to
enable these features/codecs.

Now there are 3 packages available that hopefully should satisfy most users:
* full
  This package enables all features and codecs.
* dynamic
  This package only enables PCM/AIFF and MP3 codecs and all other
  features/codecs can be added by manually installing OpenWrt packages.
* custom
  This package allows for customizing squeezelite.

Signed-off-by: Robert Högberg <robert.hogberg@gmail.com>