powerpc: ppc4xx: remove PPChameleonEVB, CATcenter boards

These boards are still non-generic boards.

It is a good thing that we can drop board-specific hack code
from drivers/mtd/nand/nand_base.c

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Stefan Roese <sr@denx.de>
Cc: Andrea "llandre" Marson <andrea.marson@dave-tech.it>