autoboot: Rename CONFIG_MENU_SHOW to include AUTOBOOT

Rename this option to CONFIG_AUTOBOOT_MENU_SHOW this it relates to the
autoboot functionality.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.bootmenu b/doc/README.bootmenu
index 34ff8d5..ca50990 100644
--- a/doc/README.bootmenu
+++ b/doc/README.bootmenu
@@ -91,7 +91,7 @@
 
   #define CONFIG_AUTOBOOT_KEYED
   #define CONFIG_BOOTDELAY 30
-  #define CONFIG_MENU_SHOW
+  #define CONFIG_AUTOBOOT_MENU_SHOW
 
 When you intend to use the bootmenu on color frame buffer console,
 make sure to additionally define CONFIG_CFB_CONSOLE_ANSI in the
diff --git a/doc/README.menu b/doc/README.menu
index 450c6a8..0f3d741 100644
--- a/doc/README.menu
+++ b/doc/README.menu
@@ -14,7 +14,7 @@
 the menu, and an opaque pointer to data controlled by the consumer.
 
 If you want to show a menu, instead starting the shell, define
-CONFIG_MENU_SHOW. You have to code the int menu_show(int bootdelay)
+CONFIG_AUTOBOOT_MENU_SHOW. You have to code the int menu_show(int bootdelay)
 function, which handle your menu. This function returns the remaining
 bootdelay.