feat(extiotest): Add testing tool for real EXTIO devices

A small but helpful tool to run a quick functional test
of a real EXTIO device connected to the target machine.

src/main/extiotest/Module.mk

@@ -0,0 +1,9 @@
+exes            += extiotest \
+
+libs_extiotest     := \
+    extiodrv \
+    extio \
+    util \
+
+src_extiotest      := \
+    main.c \