avcodec/evc_decoder: Provided support for EVC decoder

- Added EVC decoder wrapper
- Changes in project configuration file and libavcodec Makefile
- Added documentation for xevd wrapper

Signed-off-by: Dawid Kozinski <d.kozinski@samsung.com>
Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -290,6 +290,7 @@ External library support:
   --enable-libx264         enable H.264 encoding via x264 [no]
   --enable-libx265         enable HEVC encoding via x265 [no]
   --enable-libxeve         enable EVC encoding via libxeve [no]
+  --enable-libxevd         enable EVC decoding via libxevd [no]
   --enable-libxavs         enable AVS encoding via xavs [no]
   --enable-libxavs2        enable AVS2 encoding via xavs2 [no]
   --enable-libxcb          enable X11 grabbing using XCB [autodetect]
@@ -1902,6 +1903,7 @@ EXTERNAL_LIBRARY_LIST="
     libvorbis
     libvpx
     libwebp
+    libxevd
     libxeve
     libxml2
     libzimg
@@ -3460,6 +3462,7 @@ libx265_encoder_deps="libx265"
 libx265_encoder_select="atsc_a53"
 libxavs_encoder_deps="libxavs"
 libxavs2_encoder_deps="libxavs2"
+libxevd_decoder_deps="libxevd"
 libxeve_encoder_deps="libxeve"
 libxvid_encoder_deps="libxvid"
 libzvbi_teletext_decoder_deps="libzvbi"
@@ -6875,6 +6878,7 @@ enabled libx265           && require_pkg_config libx265 x265 x265.h x265_api_get
                              require_cpp_condition libx265 x265.h "X265_BUILD >= 89"
 enabled libxavs           && require libxavs "stdint.h xavs.h" xavs_encoder_encode "-lxavs $pthreads_extralibs $libm_extralibs"
 enabled libxavs2          && require_pkg_config libxavs2 "xavs2 >= 1.3.0" "stdint.h xavs2.h" xavs2_api_get
+enabled libxevd           && require_pkg_config libxevd "xevd >= 0.4.1" "xevd.h" xevd_decode
 enabled libxeve           && require_pkg_config libxeve "xeve >= 0.4.3" "xeve.h" xeve_encode
 enabled libxvid           && require libxvid xvid.h xvid_global -lxvidcore
 enabled libzimg           && require_pkg_config libzimg "zimg >= 2.7.0" zimg.h zimg_get_api_version