powerpc: Enable /dev/port when isa_io_special is set

isa_io_special is set when the platform provides a "special"
implementation of inX/outX via some FW interface for example.

Such a platform doesn't need an ISA bridge on PCI, and so /dev/port
should be made available even if one isn't present.

This makes the LPC bus IOs accessible via /dev/port on PowerNV Power8
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/io.h

@@ -21,7 +21,7 @@ extern struct pci_dev *isa_bridge_pcidev;
 /*
  * has legacy ISA devices ?
  */
-#define arch_has_dev_port()	(isa_bridge_pcidev != NULL)
+#define arch_has_dev_port()	(isa_bridge_pcidev != NULL || isa_io_special)
 #endif
 
 #include <linux/device.h>