sandbox: Implement the bootm command for sandbox

When sandbox does a 'bootm' to run a kernel we cannot actually execute it.
So just exit sandbox, which is essentially what U-Boot does on other archs.
Also, allow sandbox to use bootm on any kernel, so that it can be used
to test booting of kernels from any architecture.

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

arch/sandbox/cpu/cpu.c

@@ -8,10 +8,16 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
-int do_reset(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+void reset_cpu(ulong ignored)
 {
 	/* This is considered normal termination for now */
 	os_exit(0);
+}
+
+int do_reset(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
+{
+	reset_cpu(0);
+
 	return 0;
 }
 
@@ -28,7 +34,14 @@ unsigned long __attribute__((no_instrument_function)) timer_get_us(void)
 
 int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
 {
-	return -1;
+	if (flag & (BOOTM_STATE_OS_GO | BOOTM_STATE_OS_FAKE_GO)) {
+		bootstage_mark(BOOTSTAGE_ID_RUN_OS);
+		printf("## Transferring control to Linux (at address %08lx)...\n",
+		       images->ep);
+		reset_cpu(0);
+	}
+
+	return 0;
 }
 
 int cleanup_before_linux(void)