MPC512x: use I/O accessors instead of pointer accesses

MPC512x: use I/O accessors instead of pointer accesses

This commit changes the MPC512x code to use I/O accessor calls (i.e.
out_*() and in_*()) instead of using deprecated pointer accesses.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: John Rigby <jcrigby@gmail.com>