target-ppc: Fix target_ulong vs. hwaddr format mismatches

Since HWADDR_PRIx is always the same now, use %016 for TARGET_PPC64 and
%08 for common code. This may slightly change the ppc64 debug output.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>