powerpc/p2041rdb: remove watch dog related codes

CPLD 2.2 removed board watch dog support due to the limitation of CPLD
capacity after adding all the requested features, such as switch overriding.
There is no pin-compatible upgrade part available for current PCB design.
So remove codes related to it.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>