Devicetrees tend to become very long and it is hard to find the
interesting nodes in a full tree output.
This patch adds the -n option to the of_node command. With this
option only the names of the nodes are printed, but not the properties.
The resulting output is much shorter and the node one is interested
in can be copy/pasted to a second call to of_node.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>