bootm: Allow building bootm.c without CONFIG_SYS_BOOTM_LEN

This code cannot be compiled by boards which don't have this option. Add
an accessor in the header file to avoid another #ifdef

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>

boot/bootm.c

@@ -637,11 +637,11 @@ static int bootm_load_os(struct bootm_headers *images, int boot_progress)
 	load_buf = map_sysmem(load, 0);
 	image_buf = map_sysmem(os.image_start, image_len);
 	err = image_decomp(os.comp, load, os.image_start, os.type,
-			   load_buf, image_buf, image_len,
-			   CONFIG_SYS_BOOTM_LEN, &load_end);
+			   load_buf, image_buf, image_len, bootm_len(),
+			   &load_end);
 	if (err) {
-		err = handle_decomp_error(os.comp, load_end - load,
-					  CONFIG_SYS_BOOTM_LEN, err);
+		err = handle_decomp_error(os.comp, load_end - load, bootm_len(),
+					  err);
 		bootstage_error(BOOTSTAGE_ID_DECOMP_IMAGE);
 		return err;
 	}

include/bootm.h

@@ -89,6 +89,14 @@ struct bootm_info {
 #define bootm_x86_set(_bmi, _field, _val)
 #endif
 
+static inline ulong bootm_len(void)
+{
+#ifdef CONFIG_SYS_BOOTM_LEN
+	return CONFIG_SYS_BOOTM_LEN;
+#endif
+	return 0;
+}
+
 /**
  * bootm_init() - Set up a bootm_info struct with useful defaults
  *