xen/arm: introduce HYPERVISOR_platform_op on arm and arm64

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index ebbfa64..64f1726 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -326,5 +326,6 @@
 EXPORT_SYMBOL_GPL(HYPERVISOR_physdev_op);
 EXPORT_SYMBOL_GPL(HYPERVISOR_vcpu_op);
 EXPORT_SYMBOL_GPL(HYPERVISOR_tmem_op);
+EXPORT_SYMBOL_GPL(HYPERVISOR_platform_op);
 EXPORT_SYMBOL_GPL(HYPERVISOR_multicall);
 EXPORT_SYMBOL_GPL(privcmd_call);