arm: mvebu: x240: Don't build mkeficapsule

The x240 board doesn't use EFI and our toolchains don't include gnutls
so disable the tool in the defconfig.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/x240_defconfig b/configs/x240_defconfig
index 4fca109..5e5b467 100644
--- a/configs/x240_defconfig
+++ b/configs/x240_defconfig
@@ -77,3 +77,4 @@
 CONFIG_USB_ETHER_SMSC95XX=y
 # CONFIG_FAT_WRITE is not set
 # CONFIG_SMBIOS is not set
+# CONFIG_TOOLS_MKEFICAPSULE is not set