superio: Use 'pnp_devfn_t' over 'device_t' in romstage component

The romstage component of Super I/O support is in fact written around
passing a lower and upper half packed integer. We currently have two
typedef's for this, 'device_t' and 'pnp_devfn_t'. We wish to make use of
'pnp_devfn_t' over 'device_t' as 'device_t' changes it's typedef in the
ramstage context and so is really a conflicting definition. This helps
solve problems down the road to having the 'real' 'device_t' definition
usable in romstage later.

This follows on from the rational given in:
c2956e7 device/pci_early.c: Mixes up variants of a typedefs to 'u32'

Change-Id: Ia9f238ebb944f9fe7b274621ee0c09a6de288a76
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6231
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins)

src/superio/winbond/common/winbond.h

@@ -24,6 +24,6 @@
 #include <arch/io.h>
 #include <stdint.h>
 
-void winbond_enable_serial(device_t dev, u16 iobase);
+void winbond_enable_serial(pnp_devfn_t dev, u16 iobase);
 
 #endif /* SUPERIO_WINBOND_COMMON_ROMSTAGE_H */