Allow partial build with selected components

Allow partial build with selected components

Add --enable-* and --with-pcm-plugins configure options for partial builds.

User can choose the core components (pcm, mixer, rawmidi, hwdep, seq, instr)
via --enable-xxx or --disable-xxx option.  As default, all components are
enabled.

The PCM plugins to build can be selected via --with-pcm-plugins option.
For example, to build only rate and linear plugin, pass
  --with-pcm-plugins=rate,linear
Passing "all" will select all plugins (it's the default value).

The plug plugin will select linear and copy plugins automatically.
The other auto conversions of plug plugin are enabled only when the
corresponding plugin is selected.