rootfs.py: Don't create modules directory for all kernels

efa88e1c227d695319197f511701e0230d301f39 arranged for the versioned
modules directory to be created and depmod to run for every kernel
package. Unfortunately this happens for every _built_ kernel package,
even if that package and/or its modules aren't installed in the rootfs.

Let's assume that there's no point in running depmod if the modules
directory did not already exist.

(This problem was observed in Scarthgap and this fix was tested there.
It doesn't look like any of the subsequent changes will have affected
this behaviour.)

(From OE-Core rev: 80c218462c6e4a2deb73803a5d36e8b1f7ed5ed7)

Signed-off-by: Mike Crowe <mac@mcrowe.com>
Reviewed-by: Jack Mitchell <jack@embed.me.uk>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/rootfs.py

@@ -362,11 +362,12 @@ class Rootfs(object, metaclass=ABCMeta):
 
             versioned_modules_dir = os.path.join(self.image_rootfs, modules_dir, kernel_ver)
 
-            bb.utils.mkdirhier(versioned_modules_dir)
-
-            bb.note("Running depmodwrapper for %s ..." % versioned_modules_dir)
-            if self._exec_shell_cmd(['depmodwrapper', '-a', '-b', self.image_rootfs, kernel_ver, kernel_package_name]):
-                bb.fatal("Kernel modules dependency generation failed")
+            if os.path.exists(versioned_modules_dir):
+                bb.note("Running depmodwrapper for %s ..." % versioned_modules_dir)
+                if self._exec_shell_cmd(['depmodwrapper', '-a', '-b', self.image_rootfs, kernel_ver, kernel_package_name]):
+                    bb.fatal("Kernel modules dependency generation failed")
+            else:
+                bb.note("Not running depmodwrapper for %s since directory does not exist" % versioned_modules_dir)
 
     """
     Create devfs: