If any of these files (say A) would be changed in such a way
that A acquires a new dependency on another file B, building B
would need to be added to all the rules that lead to A being built.
Yet currently the rules for several files are spread over
the lavc Makefile and the Makefile of the lavc/hevc subdir, making
it more likely to be forgotten. So move the rules for these files
to the lavc/Makefile.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
