X86/PCI: Remove the dependency on isapnp_disable.

This looks to be vestigial dependency that had never been used even
in the original code base (2.6.18) from which this driver
was up-ported. Without this fix, with the CONFIG_ISAPNP, we get this
compile failure:

arch/x86/pci/xen.c: In function 'pci_xen_init':
arch/x86/pci/xen.c:138: error: 'isapnp_disable' undeclared (first use in this function)
arch/x86/pci/xen.c:138: error: (Each undeclared identifier is reported only once
arch/x86/pci/xen.c:138: error: for each function it appears in.)
Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/pci/xen.c

@@ -133,11 +133,6 @@ int __init pci_xen_init(void)
 	acpi_noirq = 1;
 #endif
 
-#ifdef CONFIG_ISAPNP
-	/* Stop isapnp from probing */
-	isapnp_disable = 1;
-#endif
-
 #ifdef CONFIG_PCI_MSI
 	x86_msi.setup_msi_irqs = xen_setup_msi_irqs;
 	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;