vendorcode/eltan/security: Move eltan security from chipset to security menu

The eltan security items ended up in the chipset menu which is not
desired. Now the eltan security option (when enabled in mainboard) shows
up in the security menu.

BUG=N/A
TEST=build

Change-Id: I3b2aa3836e8d9a3242c6d1f3ba7b7821a5cfb9d3
Signed-off-by: Wim Vervoorn <wvervoorn@eltan.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36851
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Frans Hendriks <fhendriks@eltan.com>

src/Kconfig

@@ -461,6 +461,7 @@ endmenu
 menu "Security"
 
 source "src/security/Kconfig"
+source "src/vendorcode/eltan/security/Kconfig"
 
 endmenu