ARM: shmobile: lager: enable nfsroot in DTS

Now that Ether support has been added to the lager board
it is possible to use nfsroot. This configuration is
in line with that of other shmobile boards.

Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>