avcodec/parser: move parsers list and related API to its own file

And add it to the CONFIGURABLE_COMPONENTS list in Makefile. This way, changes
to the new file will be tracked and the usual warning to suggest re-running
configure will be shown.

Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>