Kconfig: Provide an option for the standalone directory

Rather than using CONFIG_EXAMPLES to control the inclusion of this
directory, create a separate option. This will allow examples to be
added which don't relate to the legacy API.

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

examples/Kconfig

@@ -9,3 +9,11 @@ config EXAMPLES
 	help
 	  U-Boot provides an legacy API for standalone applications. Examples
 	  are provided in directory examples/.
+
+config EXAMPLES_STANDALONE
+	bool "Compile standalone examples"
+	depends on EXAMPLES
+	default y
+	help
+	  Build the various examples in the standalone/directory for use with
+	  the legacy API.

examples/Makefile

@@ -6,6 +6,6 @@ ifdef FTRACE
 subdir-ccflags-y += -finstrument-functions -DFTRACE
 endif
 
-subdir-y += standalone
+subdir-$(EXAMPLES_STANDALONE) += standalone
 subdir-$(CONFIG_LEGACY_API) += api
 endif