sandbox: Add -i option to enter interactive mode

Normally when U-Boot starts with a command (-c option) it quits when the
command completes. Normally this is what is requires, since the test is
likely complete.

Provide an option to jump into the console instead, so that debugging or
other tasks may be performed before quitting.

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

arch/sandbox/include/asm/state.h

@@ -7,6 +7,7 @@
 #define __SANDBOX_STATE_H
 
 #include <config.h>
+#include <stdbool.h>
 
 /* How we exited U-Boot */
 enum exit_type_id {
@@ -23,6 +24,7 @@ struct sandbox_spi_info {
 /* The complete state of the test system */
 struct sandbox_state {
 	const char *cmd;		/* Command to execute */
+	bool interactive;		/* Enable cmdline after execute */
 	const char *fdt_fname;		/* Filename of FDT binary */
 	enum exit_type_id exit_type;	/* How we exited U-Boot */
 	const char *parse_err;		/* Error to report from parsing */