barebox doesn't define a CONFIG_OF kconfig option, but CONFIG_OFTREE
for the device tree handling and CONFIG_OFDEVICE for probing devices
out of the device tree.

Replace comment mentions of CONFIG_OF with mentions of either as
appropriate.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>