The negative depends rules out using UDC for some targets of a
multi-image barebox while still supporting SAMA5D4.
We don't (yet) have such a configuration, but seeing as there is little
to gain by restricting the selection, drop it.

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