ppc64 iSeries: Move memory setup into iSeries device tree

This patch adds the required nodes to the iSeries device tree to allow
early_init_devtree() to do the lmb setup for us.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>