svt-av1-psy: limit x86_64-specific dependencies

Upstream SVT-AV1 deprecated the USE_EXTERNAL_CPUINFO option and replaced
it with USE_CPUINFO, which defaults to AUTO [1]. SVT-AV1 will use only
use the bundled version of cpuinfo if it cannot find the system version.
The use of cpuinfo was also disabled for aarch64 [2], so limit its use
to x86_64.

[1]: https://gitlab.com/AOMediaCodec/SVT-AV1/-/commit/54ac9322e79508e6ef3474d77f8e32e4ca49b923
[2]: https://gitlab.com/AOMediaCodec/SVT-AV1/-/commit/ec699561b51f3204e2df6d4c2578eea1f7bd52be

Author: al3xtjames

pkgs/by-name/sv/svt-av1-psy/package.nix

@@ -32,21 +32,26 @@ stdenv.mkDerivation (finalAttrs: {
         )
       )
       {
-        USE_EXTERNAL_CPUINFO = true;
         LIBDOVI_FOUND = true;
         LIBHDR10PLUS_RS_FOUND = true;
       };
 
-  nativeBuildInputs = [
-    cmake
-    nasm
-  ];
+  nativeBuildInputs =
+    [
+      cmake
+    ]
+    ++ lib.optionals stdenv.hostPlatform.isx86_64 [
+      nasm
+    ];
 
-  buildInputs = [
-    cpuinfo
-    libdovi
-    hdr10plus
-  ];
+  buildInputs =
+    [
+      libdovi
+      hdr10plus
+    ]
+    ++ lib.optionals stdenv.hostPlatform.isx86_64 [
+      cpuinfo
+    ];
 
   passthru.updateScript = unstableGitUpdater {
     branch = "master";