ppc/ppc405: Introduce a PPC405 SoC

ppc/ppc405: Introduce a PPC405 SoC

It is an initial model to start QOMification of the PPC405 board.
QOM'ified devices will be reintroduced one by one. Start with the
memory regions, which name prefix is changed to "ppc405".

Also, initialize only one RAM bank. The second bank is a dummy one
(zero size) which is here to match the hard coded number of banks in
ppc405ep_init().

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: <20220809153904.485018-6-clg@kaod.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>