[POWERPC] 85xx: Add cpm nodes for 8541/8555 CDS

We don't use any CPM devices on these boards, but the muram node on these
chips is different from the 8560, so it's helpful to people working with
custom boards based on these chips.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>