Allow runtime configuration of "zero-delay" check

Define the new "-2" value for bootdelay to mean autoboot with no delay
and don't check for an abort key (while "0" value means do check).

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/common/main.c b/common/main.c
index 81984ac..9507cec 100644
--- a/common/main.c
+++ b/common/main.c
@@ -222,7 +222,8 @@
 #ifdef CONFIG_MENUPROMPT
 	printf(CONFIG_MENUPROMPT);
 #else
-	printf("Hit any key to stop autoboot: %2d ", bootdelay);
+	if (bootdelay >= 0)
+		printf("Hit any key to stop autoboot: %2d ", bootdelay);
 #endif
 
 #if defined CONFIG_ZERO_BOOTDELAY_CHECK
@@ -382,7 +383,7 @@
 
 	debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");
 
-	if (bootdelay >= 0 && s && !abortboot (bootdelay)) {
+	if (bootdelay != -1 && s && !abortboot(bootdelay)) {
 # ifdef CONFIG_AUTOBOOT_KEYED
 		int prev = disable_ctrlc(1);	/* disable Control C checking */
 # endif