pnv/psi: Correct the pnv-psi* devices not to be sysbus devices

pnv/psi: Correct the pnv-psi* devices not to be sysbus devices

pnv_chip_power8_instance_init() creates a "pnv-psi-POWER8" sysbus
device in a way that leaves it unplugged.
pnv_chip_power9_instance_init() and pnv_chip_power10_instance_init()
do the same for "pnv-psi-POWER9" and "pnv-psi-POWER10", respectively.

These devices aren't actually sysbus devices.  Correct that.

Cc: "Cédric Le Goater" <[email protected]>
Cc: David Gibson <[email protected]>
Cc: [email protected]
Signed-off-by: Markus Armbruster <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Message-Id: <20200609122339[email protected]>