efivars: check for EFI_RUNTIME_SERVICES

The efivars code requires EFI runtime services to function, so check
that they are enabled.

This fixes a crash when booting with the "noefi" kernel parameter, and
also when mixing kernel and firmware "bitness", e.g. 32-bit kernel with
64-bit firmware.
Tested-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

drivers/firmware/efi/efivars.c

@@ -583,6 +583,9 @@ int efivars_sysfs_init(void)
 	struct kobject *parent_kobj = efivars_kobject();
 	int error = 0;
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES))
+		return -ENODEV;
+
 	/* No efivars has been registered yet */
 	if (!parent_kobj)
 		return 0;