Most of the systemcmds tests run in the posix build. The UART tests
fail for me as I do not have a UART connected.
Signed-off-by: Mark Charlebois <charlebm@gmail.com>
- Use distinct common symbols for px4io and px4fmu device files, and use
instead of hardcoded filenames
- Use common symbols defining px4io bits consistently between px4fmu and
px4io builds.