video/gtk4: Add dmabuf to the default features

We only ever use this feature along with checking for target platform=linux, which means it doesn't have any effect on macos and windows and thus we could try to be building the feature by default if we are on linux.

Previously the dmabuf feature depended on the wayland feature but that would try to build wayland crates on windows/macos and thus we need to remove that. In practice wayland is only a runtime dependency as the only working dmabuf platform, and the dmabuf negotiation will happen automatically if the proper conditions are met. (Running on wayland and with a Wayland context and having capable hardware and so on).