fdt: Start a test for the fdt command

Add a basic test of the 'fdt addr' command, to kick things off.

This includes a new convenience function to run a command from a printf()
string.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/command.h

@@ -257,6 +257,16 @@ int board_run_command(const char *cmdline);
 int run_command(const char *cmd, int flag);
 int run_command_repeatable(const char *cmd, int flag);
 
+/**
+ * run_commandf() - Run a command created by a format string
+ *
+ * The command cannot be larger than 127 characters
+ *
+ * @fmt: printf() format string
+ * @...: Arguments to use (flag is always 0)
+ */
+int run_commandf(const char *fmt, ...);
+
 /**
  * Run a list of commands separated by ; or even \0
  *