ARM: shmobile: henninger: add Ether DT support

Define the Henninger board dependent part of the Ether device node.
Enable DHCP and NFS root for the kernel booting.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>