I figured out that the problem is in the OF source code of the commit: Merge tag devicetree-for-4.20.
I reverted the following OF files and SMP works!

Code: Select all
drivers/of/base.c
drivers/of/device.c
drivers/of/of_mdio.c
drivers/of/of_numa.c
drivers/of/of_private.h
drivers/of/overlay.c
drivers/of/platform.c
drivers/of/unittest-data/overlay_15.dts
drivers/of/unittest-data/tests-overlay.dtsi
drivers/of/unittest.c
include/linux/of.h
Christian