orb_exists support for muorb

src/firmware/qurt/px4muorb.idl

src/modules/muorb/adsp/px4muorb.cpp

src/modules/muorb/adsp/px4muorb.hpp

src/modules/muorb/adsp/uORBFastRpcChannel.cpp

src/modules/muorb/adsp/uORBFastRpcChannel.hpp

src/modules/muorb/krait/px4muorb_KraitRpcWrapper.cpp

src/modules/muorb/krait/px4muorb_KraitRpcWrapper.hpp

src/modules/muorb/krait/uORBKraitFastRpcChannel.cpp

src/modules/muorb/krait/uORBKraitFastRpcChannel.hpp

src/modules/sdlog2/sdlog2.c

src/modules/uORB/uORBCommunicator.hpp

src/modules/uORB/uORBDevices.cpp

src/modules/uORB/uORBDevices.hpp

src/modules/uORB/uORBManager.cpp

src/modules/uORB/uORBManager.hpp