mpc8641: Change 32-bit memory map

The memory map on the 8641hpcn is modified to look more like
the 85xx boards; this is a step towards a more standardized
layout going forward. As part of this change, we now relocate
the flash.

The regions for some of the mappings were far larger than they
needed to be.  I have reduced the mappings to match the
actual sizes supported by the hardware.

In addition I have removed the comments at the head
of the BAT blocks in the config file, rather than updating
them.  These get horribly out of date, and it's a simple
matter to look at the defines to see what they are set to
since everything is right here in the same file.

Documentation has been changed to reflect the new map, as this
change is user visible, and affects the OS which runs post-uboot.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>