powerpc/p1010rdb:update mtd of nand to adapt to both old and new p1010rdb

P1010rdb-pa and p1010rdb-pb have different mtd of nand.
So update dts to adapt to both p1010rdb-pa and p1010rdb-pb.

Move the nand-mtd from p1010rdb.dtsi to p1010rdb-pa*.dts.
Remove nand-mtd for p1010rdb-pb, whick will use mtdparts
from u-boot instead of nand-mtd in device tree.

Signed-off-by: Zhao Qiang <B45475@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>