multimedia/{mplayer|mencoder}: Fix stage-qa warnings

Details:

• Rework dependencies to fix stage-qa warnings, at least for the default packages and a couple configs tested.
• Add JPEG OPTION to allow to actually disable it (as it is picked up automatically in most systems via build dependencies, even if the user does not want to include it).

PR: 256994
Reported by: bsd@philippost.de
MFH: 2022Q3