of: overlay: check prevents multiple fragments touching same property
Add test case of two fragments updating the same property. After
adding the test case, the system hangs at end of boot, after
after slub stack dumps from kfree() in crypto modprobe code.
Multiple overlay fragments adding, modifying, or deleting the same
property is not supported. Add check to detect the attempt and fail
the overlay apply.
Before this patch, the first fragment error would terminate
processing. Allow fragment checking to proceed and report all
of the fragment errors before terminating the overlay apply. This
is not a hot path, thus not a performance issue (the error is not
transient and requires fixing the overlay before attempting to
apply it again).
After applying this patch, the devicetree unittest messages will
include: