px4io: support reboot of px4io and update of fw without safety switch

this added a new PX4IO protocol operation for rebooting the IO board
and immediately uploading a new IO firmware. The timing is such that
this works with both revision 3 and revision 4 IO bootloaders
px4io: added px4io checkcrc command

this checks the IO firmware CRC against a given file, allowing for
automatic update of IO firmware via the forceupdate command