x86/geode: add missing include after rebase

The x86 image generation was refacted via cb007a7bf6 and accidently not
included `geode.mk` when selected as subtarget.

Now the file is included and image compilation for x86/geode works
again.

Thanks to Russell Senior <russell@personaltelco.net> for reporting the
problem and suggesting a patch!

Signed-off-by: Paul Spooren <mail@aparcar.org>

target/linux/x86/image/Makefile

@@ -128,6 +128,10 @@ ifeq ($(SUBTARGET),generic)
   include generic.mk
 endif
 
+ifeq ($(SUBTARGET),geode)
+  include geode.mk
+endif
+
 ifeq ($(SUBTARGET),legacy)
   include legacy.mk
 endif