sandbox: Disable standalone/API support

This is not useful on the sandbox architecture since we can simply link all
our code with U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>

Makefile

@@ -137,9 +137,7 @@ unexport CDPATH
 
 # The "tools" are needed early, so put this first
 # Don't include stuff already done in $(LIBS)
-SUBDIRS	= tools \
-	  examples/standalone \
-	  examples/api
+SUBDIRS	= tools
 
 .PHONY : $(SUBDIRS) $(VERSION_FILE) $(TIMESTAMP_FILE)
 
@@ -156,6 +154,11 @@ sinclude $(obj)include/autoconf.mk
 include $(obj)include/config.mk
 export	ARCH CPU BOARD VENDOR SOC
 
+ifndef CONFIG_SANDBOX
+SUBDIRS += examples/standalone \
+	  examples/api
+endif
+
 # set default to nothing for native builds
 ifeq ($(HOSTARCH),$(ARCH))
 CROSS_COMPILE ?=