nouveau/headers: Add initial Rust bindings

This adds the infrastructure for the nvidia_headers crate. It currently only has declarations for the texture headers but QMDs should be trivial to add as well. The plan is to organize it as follows:

crate nvidia_headers {
    mod cl9097 {
        // Methods
        mod tex {
            // Texture defines
        }
    }
    mod clc5c0 {
        // Methods
        mod qmd {
            // QMD defines
        }
    }
}