spapr: Include "pre-plugged" DIMMS in ram size calculation at reset

spapr: Include "pre-plugged" DIMMS in ram size calculation at reset

At guest reset time, we allocate a hash page table (HPT) for the guest
based on the guest's RAM size.  If dynamic HPT resizing is not available we
use the maximum RAM size, if it is we use the current RAM size.

But the "current RAM size" calculation is incorrect - we just use the
"base" ram_size from the machine structure.  This doesn't include any
pluggable DIMMs that are already plugged at reset time.

This means that if you try to start a 'pseries' machine with a DIMM
specified on the command line that's much larger than the "base" RAM size,
then the guest will get a woefully inadequate HPT.  This can lead to a
guest freeze during boot as it runs out of HPT space during initial MMU
setup.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Greg Kurz <groug@kaod.org>