autoboot: add an option to override keyed autoboot

As originally implemented, setting the AUTOBOOT_KEYED config option will
prevent users from breaking into the autoboot script with ctrl-c. Restore
that option with a new config symbol.

Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com>
diff --git a/common/main.c b/common/main.c
index 6f475f0..8b6f274 100644
--- a/common/main.c
+++ b/common/main.c
@@ -392,13 +392,13 @@
 	debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");
 
 	if (bootdelay != -1 && s && !abortboot(bootdelay)) {
-#ifdef CONFIG_AUTOBOOT_KEYED
+#if defined(CONFIG_AUTOBOOT_KEYED) && !defined(CONFIG_AUTOBOOT_KEYED_CTRLC)
 		int prev = disable_ctrlc(1);	/* disable Control C checking */
 #endif
 
 		run_command_list(s, -1, 0);
 
-#ifdef CONFIG_AUTOBOOT_KEYED
+#if defined(CONFIG_AUTOBOOT_KEYED) && !defined(CONFIG_AUTOBOOT_KEYED_CTRLC)
 		disable_ctrlc(prev);	/* restore Control C checking */
 #endif
 	}