menuconfig: Show "Barebox", not "Linux" at the top.

The menuconfig configures Barebox, not the Linux kernel, so no reason
to print "Linux" there.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Kconfig

@@ -2,7 +2,7 @@
 # For a description of the syntax of this configuration file,
 # see Documentation/kbuild/kconfig-language.txt.
 #
-mainmenu "Linux/$ARCH $KERNELVERSION Barebox Configuration"
+mainmenu "Barebox/$ARCH $KERNELVERSION Configuration"
 
 config SRCARCH
 	string