MPC512x: remove include/mpc512x.h

Move needed definitions (register descriptions etc.) from
include/mpc512x.h  into  include/asm-ppc/immap_512x.h.

Instead of using a #define'd register offset, use a function that
provides the PATA controller's base address.

All the rest of include/mpc512x.h are register offset definitions
which can be eliminated by proper use of C structures.

There are only a few register offsets remaining that are needed in
cpu/mpc512x/start.S; for these we provide cpu/mpc512x/asm-offsets.h
which is intended as a temporary workaround only. In a later patch
this file will be removed, too, and then auto-generated from the
respective C structs.

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