ppc/ppc405: QOM'ify CPU

ppc/ppc405: QOM'ify CPU

Drop the use of ppc4xx_init() and duplicate a bit of code related to
clocks in the SoC realize routine. We will clean that up in the
following patches.

ppc_dcr_init() simply allocates default DCR handlers for the CPU. Maybe
this could be done in model initializer of the CPU families needing it.

Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-Id: <20220809153904.485018-8-clg@kaod.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>