boot: Make preboot and bootcmd require CMDLINE

In order for a predefined "preboot" or "bootcmd" to be executed by the
running system we must have a command line.  Add CMDLINE as a
dependency.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/boot/Kconfig b/boot/Kconfig
index 4ce8a98..ef71883 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -1590,6 +1590,7 @@
 
 config USE_BOOTCOMMAND
 	bool "Enable a default value for bootcmd"
+	depends on CMDLINE
 	help
 	  Provide a default value for the bootcmd entry in the environment.  If
 	  autoboot is enabled this is what will be run automatically.  Enable
@@ -1609,6 +1610,7 @@
 
 config USE_PREBOOT
 	bool "Enable preboot"
+	depends on CMDLINE
 	help
 	  When this option is enabled, the existence of the environment
 	  variable "preboot" will be checked immediately before starting the