Don't unconditionally show ChromeOS options

Google ChromeOS specific options were shown in the main menu
unconditionally, even on non-ChromeOS devices. Instead, hide
these options unless CONFIG_CHROMEOS is set, and also put them
in a separate menu.

Change-Id: I75f533ed5046d6df4f7d959a0ca4c2441340ef2f
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/848
Reviewed-by: Martin Roth <martin@se-eng.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Mathias Krause <minipli@googlemail.com>

src/vendorcode/google/chromeos/Kconfig

@@ -26,6 +26,9 @@ config CHROMEOS
 	  the coreboot table. NOTE: Enabling this option on an unsupported
 	  board will most likely break your build.
 
+menu "ChromeOS"
+	depends on CHROMEOS
+
 config VBNV_OFFSET
 	hex
 	default 0x26
@@ -53,3 +56,5 @@ config CHROMEOS_RAMOOPS_RAM_SIZE
 	hex "Size of preserved RAM"
 	default 0x00100000
 	depends on CHROMEOS_RAMOOPS
+
+endmenu