powerpc/fsl-booke: Add initial B4860QDS and B4420QDS board device tree

powerpc/fsl-booke: Add initial B4860QDS and B4420QDS board device tree

B4860QDS and B4420QDS share same QDS board

* common board features have been added in b4qds.dts
* various board differences are in respective files of B4860 and B4420

Signed-off-by: Shaveta Leekha <shaveta@freescale.com>
Signed-off-by: Minghuan Lian <Minghuan.Lian@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>