nouveau: move codegen to a common higher level directory.

This allows it to be built independently of the gallium driver.

Acked-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Yusuf Khan<yusisamerican@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16763>

src/gallium/drivers/nouveau/meson.build

@@ -18,8 +18,6 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-subdir('codegen')
-
 files_libnouveau = files(
   'nouveau_buffer.c',
   'nouveau_buffer.h',

src/nouveau/meson.build

@@ -21,3 +21,5 @@
 if with_tools.contains('drm-shim')
   subdir('drm-shim')
 endif
+
+subdir('codegen')