[PATCH] ppc64: Increase sparsemem defaults

The definitions in sparsemem.h arent sufficient. We currently sell
machines with 2TB of RAM, and in order to give us room for a few years
growth lets set it to 16TB.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>