powerpc: Move memory size print into common show_cpuinfo for 32-bit

Most of the platforms were printing the size of the memory
in their show_cpuinfo implementations. This moves that to
the common show_cpuinfo, so that all 32-bit platforms will
now print the size of memory.  I also update the code
to deal with the fact that total_memory is now a phys_addr_t.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>