[Toybox] cpio and duplicate directories

[enh]

i don't _think_ there's been a bug report beyond the discussion on
https://android-review.googlesource.com/c/platform/test/vts-testcase/kernel/+/2477517,
so repeating it here...

"""
The Toybox version of cpio doesn't allow duplicated directories. This
is however not a problem at all for the kernel or other archive
extraction implementations. Workaround that limitation with the option
-u which enforces files deletion and also has the side-effect of not failing
when a folder already exists.
"""

"""
This does not relate to the dev nodes but to the folder dev/ which is
added twice for different orthogonal reasons.

For some reasons toybox's CPIO does not support this by default unless
-u is set. (contrary to other implementations)
"""

(fwiw, i thought we were sorting all the inputs to all our rules, so
presumably in the kernel build we could change the `sort` to a `sort
-u`, but if this is a behavior difference from non-toybox cpio, that's
presumably still a bug rob would want to hear about anyway....)