rm9200 lowevel_init: don't touch reserved/readonly registers

For some reason the AT91rm9200 lowlevel init writes to a bunch of
reserved or read-only addresses.  All the boards seem to define the
value-to-be-written values as zero ... but they shouldn't actually
be writing *anything* there.

No documented erratum justifies these accesses.  It looks like maybe
some pre-release BDI-2000 setup code has been carried along by cargo
cult programming since at least late 2004 (per GIT history).

Here's a patch disabling what seems to be bogosity.  Tested on a
csb337; there were no behavioral changes.

Signed-off-by: David Brownell <david-b@pacbell.net>
on RM9200ek
Tested-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>