arm/xen: Drop the definition of xen_pci_platform_unplug

The commit 6f6c15ef "xen/pvhvm: Remove
the xen_platform_pci int." makes the x86 version of
xen_pci_platform_unplug static.

Therefore we don't need anymore to define a dummy xen_pci_platform_unplug
for ARM.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

arch/arm/xen/enlighten.c

@@ -45,9 +45,6 @@ static struct vcpu_info __percpu *xen_vcpu_info;
 unsigned long xen_released_pages;
 struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
 
-int xen_platform_pci_unplug = XEN_UNPLUG_ALL;
-EXPORT_SYMBOL_GPL(xen_platform_pci_unplug);
-
 static __read_mostly unsigned int xen_events_irq;
 
 static __initdata struct device_node *xen_node;