pseries: Rearrange versioned machine type code

pseries: Rearrange versioned machine type code

hw/ppc/spapr.c has a number of definitions related to the various versioned
machine types ("pseries-2.1" .. "pseries-2.5") it defines.  These are
mostly arranged by type of function first, then machine version second, and
it's not consistent about whether it goes in increasing or decreasing
version order.

This rearranges the code to keep all the definitions for a particular
machine version together, and arrange then consistently in order most
recent to least recent.

This brings us closer to matching the way PC does things, and makes later
cleanups easier to follow.

Apart from adding some comments marking each section, this is a pure
mechanical rearrangement with no semantic changes.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>