Update all relevant PowerPC entries as follows:

- Nick Piggin is promoted to Maintainer in all qemu-ppc subsystems.
  Nick has  been a solid contributor for the last couple of years and
  has the required knowledge and motivation to drive the boat.

- Greg Kurz is being removed from all qemu-ppc entries. Greg has moved
  to other areas of interest and will retire from qemu-ppc.  Thanks Mr
  Kurz for all the years of service.

- David Gibson was removed as 'Reviewer' from PowerPC TCG CPUs and PPC
  KVM CPUs. Change done per his request.

- Daniel Barboza downgraded from 'Maintainer' to 'Reviewer' in sPAPR and
  PPC KVM CPUs. It has been a long since I last touched those areas and
  it's not justified to be kept as maintainer in them.

- Cedric Le Goater and Daniel Barboza removed as 'Reviewer' in VOF. We
  don't have the required knowledge to justify it.

- VOF support downgraded from 'Maintained' to 'Odd Fixes' since it
  better reflects the current state of the subsystem.

Acked-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Message-ID: <20230915110507.194762-1-danielhb413@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>