image: Move common image code to image_board and command

We should use the cmd/ directory for commands rather than for common code
used elsewhere in U-Boot. Move the common 'source' code into
image-board.c to achieve this.

The image_source_script() function needs to call run_command_list()  so
seems to belong better in the command library. Move and rename it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/command.h b/include/command.h
index 966fd23..3c6132e 100644
--- a/include/command.h
+++ b/include/command.h
@@ -279,6 +279,18 @@
  * Return: 0 on success, or != 0 on error.
  */
 int run_command_list(const char *cmd, int len, int flag);
+
+/**
+ * cmd_source_script() - Execute a script
+ *
+ * Executes a U-Boot script at a particular address in memory. The script should
+ * have a header (FIT or legacy) with the script type (IH_TYPE_SCRIPT).
+ *
+ * @addr: Address of script
+ * @fit_uname: FIT subimage name
+ * Return: result code (enum command_ret_t)
+ */
+int cmd_source_script(ulong addr, const char *fit_uname, const char *confname);
 #endif	/* __ASSEMBLY__ */
 
 /*