include/device/device.h: Deduplicate '*_pnp_devfn_t' typedefs

'pci_devfn_t' and 'pnp_devfn_t' are already defined in arch/io.h

Change-Id: I006182bf6933fae21fe6671659b76e7031e74b71
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6230
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins)