85xx: Ensure BSS segment isn't linked at address 0

When U-Boot is relocated from flash to RAM pointers are modified
accordingly.  However, pointers initialzed with NULL values should not
be modified so that they maintain their intended NULL value.  If the
BSS segment is linked at address 0 its address will not be
updated as necessary during relocation.

This is a temporary workaround.  The end goal is to add support to
U-Boot to dynamically locate the BSS at an arbitrary address at
runtime.  When the ability to fixup the BSS inteligently is
added, this workaround can be removed and the 85xx link script
can put the BSS at a fixed address at link time.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>