ppc: e500: switch E500 based machines to full machine definition

ppc: e500: switch E500 based machines to full machine definition

Convert PPCE500Params to PCCE500MachineClass which it essentially is,
and introduce PCCE500MachineState to keep track of E500 specific
state instead of adding global variables or extra parameters to
functions when we need to keep data beyond machine init
(i.e. make it look like typical fully defined machine).

It's pretty shallow conversion instead of currently used trivial
DEFINE_MACHINE() macro. It adds extra 60LOC of boilerplate code
of full machine definition.

The patch on top[1] will use PCCE500MachineState to keep track of
platform_bus device and add E500Plate specific machine class
to use HOTPLUG_HANDLER for explicitly initializing dynamic
sysbus devices at the time they are added instead of delaying
it to machine done time by platform_bus_init_notify() which is
being removed.

1)  <1523551221[email protected]>

Signed-off-by: Igor Mammedov <[email protected]>
Suggested-by: David Gibson <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: David Gibson <[email protected]>