UPDATE: libavif 0.9.0

Here is an update to libavif 0.9.0.


## [0.9.0] - 2021-02-22

### Added
* Image grid encoding
* Premultiplied alpha support (tongyuantongyu)
* avifenc: Image grid encoding (`-g`, `--grid`)
* avifenc: Harvest framerate from y4m headers as the "default", if present
* avifenc: Recognize the Y4M format string "C420mpeg2" (wantehchang)
* Basic deduplication when writing mdat chunks

### Changed
* avifenc: Adjusted min/max/speed/fps defaults
* Better handling for export headers (tongyuantongyu)
* Use procedure specified in H.273 to quantize YUV (tongyuantongyu)
* Impose a maximum of 4096 bytes on searchSampleSize (wantehchang, fixes oss-fuzz perf issue / timeout)
* Update aom.cmd: v2.0.2
* Update dav1d.cmd: 0.8.2
* Update libgav1.cmd: 4a89dc3 / lts_2020_09_23
* Update rav1e.cmd: 0.4
* Update svt.cmd/svt.sh: v0.8.6
* Force libjpeg to output in RGB Colorspace (bugfix)
* Minor other compilation/linking/formatting/comment fixes


Index: Makefile
===================================================================
RCS file: /home/cvs/ports/graphics/libavif/Makefile,v
retrieving revision 1.14
diff -u -p -u -p -r1.14 Makefile
--- Makefile 14 Dec 2020 06:29:17 -0000 1.14
+++ Makefile 4 Mar 2021 00:09:09 -0000
@@ -4,10 +4,10 @@ COMMENT= library for encoding and decodi

GH_ACCOUNT= AOMediaCodec
GH_PROJECT= libavif
-GH_TAGNAME= v0.8.4
+GH_TAGNAME= v0.9.0
CATEGORIES= graphics

-SHARED_LIBS= avif 3.2
+SHARED_LIBS= avif 4.0

HOMEPAGE= https://github.com/AOMediaCodec/libavif

Index: distinfo
===================================================================
RCS file: /home/cvs/ports/graphics/libavif/distinfo,v
retrieving revision 1.10
diff -u -p -u -p -r1.10 distinfo
--- distinfo 14 Dec 2020 06:29:17 -0000 1.10
+++ distinfo 4 Mar 2021 00:06:26 -0000
@@ -1,2 +1,2 @@
-SHA256 (libavif-0.8.4.tar.gz) = EWtGqaSXxu8XjFoguRLYrAL4iNyMU35AtdFnAII6mxY=
-SIZE (libavif-0.8.4.tar.gz) = 2952844
+SHA256 (libavif-0.9.0.tar.gz) = 6hYD/Bjn3SDPAfC0BRVldohuy134TbjA6HGHzS+KAPQ=
+SIZE (libavif-0.9.0.tar.gz) = 2961252