serial: parisc: GSC: fix build when IOSAPIC is not set

There is a build error when using a kernel .config file from
'kernel test robot' for a different build problem:

hppa64-linux-ld: drivers/tty/serial/8250/8250_gsc.o: in function `.LC3':
(.data.rel.ro+0x18): undefined reference to `iosapic_serial_irq'

when:
  CONFIG_GSC=y
  CONFIG_SERIO_GSCPS2=y
  CONFIG_SERIAL_8250_GSC=y
  CONFIG_PCI is not set
    and hence PCI_LBA is not set.
  IOSAPIC depends on PCI_LBA, so IOSAPIC is not set/enabled.

Make the use of iosapic_serial_irq() conditional to fix the build error.

Signed-off-by: Randy Dunlap <[email protected]>
Reported-by: kernel test robot <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: [email protected]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: [email protected]
Cc: Jiri Slaby <[email protected]>
Cc: Johan Hovold <[email protected]>
Suggested-by: Helge Deller <[email protected]>
Signed-off-by: Helge Deller <[email protected]>
Cc: [email protected]
Signed-off-by: Helge Deller <[email protected]>

Author: rddunlap

drivers/tty/serial/8250/8250_gsc.c

@@ -26,7 +26,7 @@ static int __init serial_init_chip(struct parisc_device *dev)
 	unsigned long address;
 	int err;
 
-#ifdef CONFIG_64BIT
+#if defined(CONFIG_64BIT) && defined(CONFIG_IOSAPIC)
 	if (!dev->irq && (dev->id.sversion == 0xad))
 		dev->irq = iosapic_serial_irq(dev);
 #endif