By default the runtime would bind the n TVM threads (specified in TVM_NUM_THREADS) to core 0 to n-1. TVM_BIND_THREADS=0 will instead rely on the OS to schedule the threads. However, the actual behavior may look similar with or without binding. In your case, I believe TVM_NUM_THREADS=2 TVM_BIND_THREADS=1 should work.
Specifying big is for ARM CPUs with big.LITTLE cores.
More info may be found here.