powerpc/86xx: Update GE Fanuc sbc310 DTS

Update GE Fanuc DTS to match the alterations suggested during the merge of
the ppc9a DTS in commit 740d36ae

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>