Move finalize directory into a new romfs folder

The script expects a `finalize` directory in the root of romfs, which
is where all the files are.

3dstool is simple-minded; when specified a folder as the romfs target,
that folder becomes the root of romfs. This causes the built romfs to
have no `finalize` directory.

Move `finalize` to `romfs/finalize` and use the `romfs` directory for
3dstool.

Makefile

@@ -6,7 +6,7 @@ builds:
 	@[ -d builds ] || mkdir -p builds
 
 builds/finalize.romfs: builds
-	@3dstool -c -t romfs --romfs-dir finalize --file $@
+	@3dstool -c -t romfs --romfs-dir romfs --file $@
 
 builds/finalize_helper.firm: builds/finalize.romfs
 	@cp finalize_helper.gm9 GodMode9/data/autorun.gm9