General cleanup of this port

Don't add libraries as dependencies and disable them later on in configure
arguments (curl and (lib)samplerate). Enabled from now on.
Fix dependencies and functionality provided by external libraries. If we link
(lib)ffmpeg we don't need to have external libraries for handling formats
that ffmpeg already handles.
Update PKG_MD5SUM (deprecated) to PKG_HASH

Sources:
https://github.com/mir-ror/moc/blob/master/decoder_plugins/ffmpeg/ffmpeg.c#L213

Signed-off-by: Daniel Engberg <daniel.engberg.lists@pyret.net>