powerpc: Force printing of 'total_memory' to unsigned long long

total_memory is a 'phys_addr_t', Which can be either 64 or 32 bits.
Force printing as unsigned long long to silence the warning.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>