spl: Avoid #ifdef with CONFIG_SPL_PAYLOAD_ARGS_ADDR

Move the condition to the header file to improve readability.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 530ade5..8ed2eeb 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -806,9 +806,8 @@
 	}
 
 	memset(&spl_image, '\0', sizeof(spl_image));
-#ifdef CONFIG_SPL_PAYLOAD_ARGS_ADDR
-	spl_image.arg = (void *)CONFIG_SPL_PAYLOAD_ARGS_ADDR;
-#endif
+	if (IS_ENABLED(CONFIG_SPL_OS_BOOT))
+		spl_image.arg = (void *)SPL_PAYLOAD_ARGS_ADDR;
 	spl_image.boot_device = BOOT_DEVICE_NONE;
 	board_boot_order(spl_boot_list);
 
@@ -865,9 +864,8 @@
 #if CONFIG_IS_ENABLED(OS_BOOT)
 	case IH_OS_LINUX:
 		debug("Jumping to Linux\n");
-#if defined(CONFIG_SPL_PAYLOAD_ARGS_ADDR)
-		spl_fixup_fdt((void *)CONFIG_SPL_PAYLOAD_ARGS_ADDR);
-#endif
+		if (IS_ENABLED(CONFIG_SPL_OS_BOOT))
+			spl_fixup_fdt((void *)SPL_PAYLOAD_ARGS_ADDR);
 		spl_board_prepare_for_linux();
 		jump_to_image_linux(&spl_image);
 #endif