platforms: link libatomic only on emlid navio2 (raspberry pi)
platforms: link libatomic only on emlid navio2 (raspberry pi)

Linking to libatomic is only required for targets such as Raspberry Pi but not on for normal x86/x86_64 Linux builds.
PX4/Firmware,PX4/Firmware,acfloria/Firmware,krbeverx/Firmware,PX4/Firmware,acfloria/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware