alsa: setup mirrors for src downloads (#41761)

This commit adds a list of supported mirrors for all alsa projects, as described
on the download section of the alsa-project hompage:
http://alsa-project.org/main/index.php/Download

pkgs/os-specific/linux/alsa-firmware/default.nix

@@ -4,10 +4,7 @@ stdenv.mkDerivation rec {
   name = "alsa-firmware-1.0.29";
 
   src = fetchurl {
-    urls = [
-      "ftp://ftp.alsa-project.org/pub/firmware/${name}.tar.bz2"
-      "http://alsa.cybermirror.org/firmware/${name}.tar.bz2"
-    ];
+    url = "mirror://alsa/firmware/${name}.tar.bz2";
     sha256 = "0gfcyj5anckjn030wcxx5v2xk2s219nyf99s9m833275b5wz2piw";
   };
 
@@ -28,7 +25,7 @@ stdenv.mkDerivation rec {
   '';
 
   meta = {
-    homepage = http://www.alsa-project.org/main/index.php/Main_Page;
+    homepage = http://www.alsa-project.org/;
     description = "Soundcard firmwares from the alsa project";
     license = stdenv.lib.licenses.gpl2Plus;
     platforms = stdenv.lib.platforms.linux;