ffmpeg: add LibreELEC's Kodi compatibility patches

ffmpeg: add LibreELEC's Kodi compatibility patches

Patches:
  110-libdav1d-get-format: carried over from LibreELEC (Lukas Rusak):
    adds a get_format callback to the libdav1d decoder so Kodi's
    hardware-first, software-fallback decoder setup initialises
    multithreaded software decoding properly; without effect until the
    libdav1d option is enabled
  111-swscale-yuv2rgb-no-warning: carried over from LibreELEC
    (Christian Hewitt): removes the warning swscale logs on every
    context initialisation without an accelerated colourspace
    conversion

LibreELEC keeps both in one file
(packages/multimedia/ffmpeg/patches/libreelec/0001-libreelec.patch as
of LibreELEC commit 5d54b2dd82); they are split here so each keeps its
own header. Headers unchanged, hunks refreshed with quilt; the patched
tree is identical to the one LibreELEC's file produces.

Signed-off-by: Mirko Vogt <redacted>