sandbox: Don't try distro_bootcmd by default

For the distro_bootcmds to succeed on the sandbox a bit of setup is
required (e.g. network configured or host image bound), so running them
by default isn't that useful.

Add a -b/--boot command to the sandbox binary, which triggers the
distro_bootcmds to run after the other command-line commands.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Acked-by: Simon Glass <sjg@chromium.org>

arch/sandbox/include/asm/state.h

@@ -42,6 +42,7 @@ struct sandbox_spi_info {
 struct sandbox_state {
 	const char *cmd;		/* Command to execute */
 	bool interactive;		/* Enable cmdline after execute */
+	bool run_distro_boot;		/* Automatically run distro bootcommands */
 	const char *fdt_fname;		/* Filename of FDT binary */
 	const char *parse_err;		/* Error to report from parsing */
 	int argc;			/* Program arguments */