Update tune_relay_vta.py to support single board (apache#7100)

- support single pynq board run, change is credited to 'https://github.com/i24361's change, https://github.com/i24361/incubator-tvm/blob/0472b1f347976229a29be8a6e60b626a0604c8df/vta/tutorials/autotvm/tune_relay_vta_with_one_board.py
- fixes the save fail
- issues and changes are discussed in https://discuss.tvm.apache.org/t/vta-workaround-for-autotuning-with-one-pynq-z1-board/8091/9

vta/tutorials/autotvm/tune_relay_vta.py

@@ -340,18 +340,6 @@ def _topi_nn_conv2d(*args, **kwargs):
 
 def tune_and_evaluate(tuning_opt):
 
-    if env.TARGET != "sim":
-        # Get remote from fleet node
-        remote = autotvm.measure.request_remote(
-            env.TARGET, tracker_host, tracker_port, timeout=10000
-        )
-        # Reconfigure the JIT runtime and FPGA.
-        vta.reconfig_runtime(remote)
-        vta.program_fpga(remote, bitstream=None)
-    else:
-        # In simulation mode, host the RPC server locally.
-        remote = rpc.LocalSession()
-
     # Register VTA tuning tasks
     register_vta_tuning_tasks()
 
@@ -407,6 +395,19 @@ def tune_and_evaluate(tuning_opt):
     print("Tuning...")
     tune_tasks(tasks, **tuning_opt)
 
+    # evaluate with tuning history
+    if env.TARGET != "sim":
+        # Get remote from fleet node
+        remote = autotvm.measure.request_remote(
+            env.TARGET, tracker_host, tracker_port, timeout=10000
+        )
+        # Reconfigure the JIT runtime and FPGA.
+        vta.reconfig_runtime(remote)
+        vta.program_fpga(remote, bitstream=None)
+    else:
+        # In simulation mode, host the RPC server locally.
+        remote = rpc.LocalSession()
+
     # compile kernels with history best records
     with autotvm.tophub.context(target, extra_files=[log_file]):
         # Compile network
@@ -425,9 +426,9 @@ def tune_and_evaluate(tuning_opt):
         # Export library
         print("Upload...")
         temp = utils.tempdir()
-        lib.save(temp.relpath("graphlib.o"))
-        remote.upload(temp.relpath("graphlib.o"))
-        lib = remote.load_module("graphlib.o")
+        lib.export_library(temp.relpath("graphlib.tar"))
+        remote.upload(temp.relpath("graphlib.tar"))
+        lib = remote.load_module("graphlib.tar")
 
         # Generate the graph runtime
         ctx = remote.ext_dev(0) if device == "vta" else remote.cpu(0)