makefile: add makefile to compile the digi apix examples

Signed-off-by: Francisco Gil Martinez <francisco.gilmartinez@digi.com>

Makefile

@@ -0,0 +1,26 @@
+#
+# Copyright (c) 2017 Digi International Inc.
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+# OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+# PERFORMANCE OF THIS SOFTWARE.
+#
+
+SUBDIRS := apix-gpio-example apix-i2c-example apix-pwm-example apix-spi-example
+
+all: $(SUBDIRS)
+
+.PHONY: $(SUBDIRS)
+$(SUBDIRS):
+	$(MAKE) -C $@
+
+install clean:
+	for a in $(SUBDIRS); do $(MAKE) -C $$a $@; done