ARM: Kirkwood: update Network Space Mini v2 description

LaCie has released two products under the CloudBox name. The
netspace_mini_v2 machine is embedded in the oldest product. The cloudbox
machine is embedded in the newest one. In order to allow a CloudBox user
to select the right machine support, this patch adds some informations
to the netspace_mini_v2 Kconfig description. A comment is also added to
the dts file.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>