The options in vd_lavc are all related, but they don't all require the
same thing for runtime changes. To avoid having to manually add UPDATE_*
to every single option flag, the options can be split into two separate
structs. The vd_lavc_conf becomes a catch all for all the --vd-lavc
options that require the full UPDATE_VD flag. The rest of the options
are split off into the new hwdec_conf instead. Additionally,
--vd-lavc-software-fallback is renamed to --hwdec-software-fallback and
moved to the hwdec_conf as well. The new name better reflects what it
does and it logically fits with those more. UPDATE_* flags are added on
everything now so these should all now be changeable on runtime.
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