ARM64: XEN: Add a function to initialize Xen specific UEFI runtime services

When running on Xen hypervisor, runtime services are supported through
hypercall. Add a Xen specific function to initialize runtime services.

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Julien Grall <julien.grall@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>

drivers/xen/Kconfig

@@ -275,7 +275,7 @@ config XEN_HAVE_PVMMU
 
 config XEN_EFI
 	def_bool y
-	depends on X86_64 && EFI
+	depends on (ARM || ARM64 || X86_64) && EFI
 
 config XEN_AUTO_XLATE
 	def_bool y