mpg123: upgrade to 1.19.0

- switched to ${BP} variable;
- ${S} redundant, removed;
- option with-module-suffix=.so: load modules with .so extension;
- .la files are kept only for dev packages;
- clearer COPYING file, about contribution and licenses;
  no changes to licenses.

Signed-off-by: Cristian Iorga <ubik3000@gmail.com>
Signed-off-by: Cristian Iorga <cristian.iorga@intel.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>