Sensors are just a part of uORB, and there are many virtual topics used
within uORB as well. For the library apps/system/uorb/, the nuttx/uorb.h
version is more preferable. So, move public type and definition to
nuttx/uorb.h.
Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>