kconfig: Add API kconfig file

Add kconfig file to enable API support

Signed-off-by: Emmanuel Vadot <manu@bidouilliste.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Kconfig

@@ -308,6 +308,8 @@ config ARCH_FIXUP_FDT_MEMORY
 
 endmenu		# Boot images
 
+source "api/Kconfig"
+
 source "common/Kconfig"
 
 source "cmd/Kconfig"

api/Kconfig

+menu "API"
+
+config API
+	bool "Enable U-Boot API"
+	default n
+	help
+	  This option enables the U-Boot API. See api/README for more information.
+
+endmenu