Change directory structure to align with Atmel softpack

This way we can easily check with 'diff' for differences in our code and
Atmel softpack.  Also, this layout is more suitable for building various
different firmware images (e.g. factory-test, dfu-loader, main
application) for a variety of different boards (simtrace, owhw, qmod).

firmware/libboard/common/include/boardver_adc.h

@@ -0,0 +1,3 @@
+#pragma once
+
+int get_board_version_adc(void);