ppc/pnv: add helpers for pnv-phb user devices

ppc/pnv: add helpers for pnv-phb user devices

pnv_parent_qom_fixup() and pnv_parent_bus_fixup() are versions of the
helpers that were reverted by commit 9c10d86fee "ppc/pnv: Remove
user-created PHB{3,4,5} devices". They are needed to amend the QOM and
bus hierarchies of user created pnv-phbs, matching them with default
pnv-phbs.

A new helper pnv_phb_user_device_init() is created to handle
user-created devices setup. We're going to call it inside
pnv_phb_realize() in case we're realizing an user created device. This
will centralize all user device realated in a single spot, leaving the
realize functions of the phb3/phb4 backends untouched.

Another helper called pnv_chip_add_phb() was added to handle the
particularities of each chip version when adding a new PHB.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>
Message-Id: <20220811163950.578927-5-danielhb413@gmail.com>