pkgs/qemu: add qemu_full package

qemu_full enables samba and ceph support because otherwise enabling
them triggers recompilation of qemu package that takes a long time.
Similar options can be enabled later on. qemu_full is based on complete
qemu package, so hostCpuOnly is not enabled.

pkgs/top-level/all-packages.nix

@@ -18870,6 +18870,7 @@ in
   prototool = callPackage ../development/tools/prototool { };
 
   qemu_kvm = lowPrio (qemu.override { hostCpuOnly = true; });
+  qemu_full = lowPrio (qemu.override { smbdSupport = true; cephSupport = true; });
 
   # See `xenPackages` source for explanations.
   # Building with `xen` instead of `xen-slim` is possible, but makes no sense.