libva: depend on libxcb independently of libx11 propagating it

Changed files
+2
pkgs
development
libraries
libva
+2
pkgs/development/libraries/libva/default.nix
···
libdrm,
minimal ? false,
libX11,
+
libxcb,
libXext,
libXfixes,
wayland,
···
]
++ lib.optionals (!minimal) [
libX11
+
libxcb
libXext
libXfixes
wayland