hw/ppc/spapr.c: cleaning up qdev_get_machine() calls

hw/ppc/spapr.c: cleaning up qdev_get_machine() calls

This patch removes the qdev_get_machine() calls that are made in
spapr.c in situations where we can get an existing pointer for
the MachineState by either passing it as an argument to the function
or by using other already available pointers.

The following changes were made:

- spapr_node0_size: static function that is called two times:
at spapr_setup_hpt_and_vrma and ppc_spapr_init. In both cases we can
pass an existing MachineState pointer to it.

- spapr_build_fdt: MachineState pointer can be retrieved from
the existing sPAPRMachineState pointer.

- spapr_boot_set: the opaque in the first arg is a sPAPRMachineState
pointer as we can see inside ppc_spapr_init:

    qemu_register_boot_set(spapr_boot_set, spapr);

We can get a MachineState pointer from it.

- spapr_machine_device_plug and spapr_machine_device_unplug_request: the
MachineState, sPAPRMachineState, MachineClass and sPAPRMachineClass pointers
can all be retrieved from the HotplugHandler pointer.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>