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 <mirko-openwrt@nanl.de>

multimedia/ffmpeg/patches/110-libdav1d-get-format.patch

@@ -0,0 +1,46 @@
+From 342b6ab899e9c66286239c0717ea67183af505df Mon Sep 17 00:00:00 2001
+From: Lukas Rusak <lorusak@gmail.com>
+Date: Wed, 10 Apr 2019 13:39:21 -0700
+Subject: [PATCH 1/2] libavcodec/libdav1d: add libdav1d_get_format method to
+ call ff_get_format
+
+This will allow applications to properly init the decoder in
+cases where a hardware decoder is tried first and and software
+decoder is tried after by calling the get_format callback.
+
+Even though there is no hardware pixel formats available
+we still need to return the software pixel format.
+
+Tested with Kodi by checking if multithreaded software
+decoding is properly activated.
+---
+ libavcodec/libdav1d.c | 11 +++++++++++
+ 1 file changed, 11 insertions(+)
+
+--- a/libavcodec/libdav1d.c
++++ b/libavcodec/libdav1d.c
+@@ -67,6 +67,16 @@ static const enum AVPixelFormat pix_fmt_
+     AV_PIX_FMT_GBRP, AV_PIX_FMT_GBRP10, AV_PIX_FMT_GBRP12,
+ };
+ 
++static enum AVPixelFormat libdav1d_get_format(AVCodecContext *avctx, const Dav1dPicture *p)
++{
++   enum AVPixelFormat pix_fmts[2], *fmt = pix_fmts;
++
++   *fmt++ = pix_fmt[p->p.layout][p->seq_hdr->hbd];
++   *fmt = AV_PIX_FMT_NONE;
++
++   return ff_get_format(avctx, pix_fmts);
++}
++
+ static void libdav1d_log_callback(void *opaque, const char *fmt, va_list vl)
+ {
+     AVCodecContext *c = opaque;
+@@ -410,6 +420,7 @@ static int libdav1d_receive_frame(AVCode
+     if (res < 0)
+         goto fail;
+ 
++    frame->format = c->pix_fmt = libdav1d_get_format(c, p);
+     frame->width = p->p.w;
+     frame->height = p->p.h;
+     if (c->width != p->p.w || c->height != p->p.h) {

multimedia/ffmpeg/patches/111-swscale-yuv2rgb-no-warning.patch

@@ -0,0 +1,22 @@
+From b8edcb3683570867864a3d26253c4e48be51baab Mon Sep 17 00:00:00 2001
+From: chewitt <github@chrishewitt.net>
+Date: Sun, 11 Aug 2019 07:08:19 +0000
+Subject: [PATCH 2/2] add long-term yuv2rgb logging patch
+
+---
+ libswscale/yuv2rgb.c | 4 ----
+ 1 file changed, 4 deletions(-)
+
+--- a/libswscale/yuv2rgb.c
++++ b/libswscale/yuv2rgb.c
+@@ -575,10 +575,6 @@ SwsFunc ff_yuv2rgb_get_func_ptr(SwsInter
+     if (t)
+         return t;
+ 
+-    av_log(c, AV_LOG_WARNING,
+-           "No accelerated colorspace conversion found from %s to %s.\n",
+-           av_get_pix_fmt_name(c->opts.src_format), av_get_pix_fmt_name(c->opts.dst_format));
+-
+     if (c->opts.src_format == AV_PIX_FMT_YUV422P) {
+         switch (c->opts.dst_format) {
+         case AV_PIX_FMT_BGR48BE: