powerpc/85xx: Rework P1023RDS device tree

Utilize new split between board & SoC, and new SoC device trees split
into pre & post utilizing 'template' includes for SoC IP blocks.

Other changes include:
* Moved to specifying interrupt-parent for mpic at root
* Moved to 4-cell mpic interrupt cells to support MPIC timers
* Dropping "fsl,p1023-IP..." from compatibles for standard blocks
* Removed incorrect power/pmc node, there are no etsec on P1023

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>