of: Export of_remove_property() to modules

We will need to remove some OF properties in drivers/net/dsa/bcm_sf2.c
with a subsequent commit. Export of_remove_property() to modules so we
can keep bcm_sf2 modular and provide an empty stub for when CONFIG_OF is
disabled to maintain the ability to compile test.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>