ARM: XEN: Move xen_early_init() before efi_init()

Move xen_early_init() before efi_init(), then when calling efi_init()
could initialize Xen specific UEFI.

Check if it runs on Xen hypervisor through the flat dts.

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

arch/arm64/kernel/setup.c

@@ -257,6 +257,7 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	cpu_uninstall_idmap();
 
+	xen_early_init();
 	efi_init();
 	arm64_memblock_init();
 
@@ -281,8 +282,6 @@ void __init setup_arch(char **cmdline_p)
 	else
 		psci_acpi_init();
 
-	xen_early_init();
-
 	cpu_read_bootcpu_ops();
 	smp_init_cpus();
 	smp_build_mpidr_hash();