[POWERPC] Fix parse_drconf_memory() for 64-bit start addresses

Some new machines use the "ibm,dynamic-reconfiguration-memory" property
to provide memory layout information, rather than via memory nodes.

There is a bug in the code to parse this property for start addresses
over 4GB; we store the start address in an unsigned int, which means
we throw away the high bits and add apparently duplicate regions.
This results in a BUG() in free_bootmem_core().  This fixes it by
using an unsigned long instead.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>