PCI: Turn pcibios_penalize_isa_irq() into a weak function

pcibios_penalize_isa_irq() is only implemented by x86 now, and legacy ISA
is not used by some architectures.  Make pcibios_penalize_isa_irq() a
__weak function to simplify the code.  This removes the need for new
platforms to add stub implementations of pcibios_penalize_isa_irq().

[bhelgaas: changelog, comments]
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 84182b1..018877b 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1578,6 +1578,7 @@
 				 enum pcie_reset_state state);
 int pcibios_add_device(struct pci_dev *dev);
 void pcibios_release_device(struct pci_dev *dev);
+void pcibios_penalize_isa_irq(int irq, int active);
 
 #ifdef CONFIG_HIBERNATE_CALLBACKS
 extern struct dev_pm_ops pcibios_pm_ops;