powerpc/85xx: Removed P1/P2 RDB RevB support

RevB boards never really made it outside of Freescale and have been
replaced with RevC & RevD which had various board bug fixes.

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>