ppc/pnv: Remove PHB4 reset handler

The PHB4 reset handler was preparing ground for PHB5 to set
appropriately the device id. We don't need it for the PHB4 since the
device id is already set in the root port complex. PH5 will introduce
its own.

"device-id" property is now useless. It should be removed.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20211222063817.1541058-3-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>