Fix autotuning, broken in #7337

[areusch]

Turns out we have no AutoTVM integration tests at main that actually assert on anything. Adding one and fixing my breakage.

Still TODO: need to fix test_tuning_gpu, which has been failing for some time now. I don't know how to do this and it would be great if someone familiar with CUDA could debug the error:

DEBUG    autotvm:tuner.py:163 No: 1     GFLOPS: 0.00/0.00       result: MeasureResult(costs=(InstantiationError('Traceback (most recent call last):\n  [bt] (4) /workspace/build/libtvm.so(TVMFuncCall+0x61) [0x7fd90af1c2f1]\n  [bt] (3) /workspace/build/libtvm.so(+0x78e326) [0x7fd90a1eb326]\n  [bt] (2) /workspace/build/libtvm.so(tvm::transform::SequentialNode::operator()(tvm::IRModule, tvm::transform::PassContext const&) const+0x3ed) [0x7fd90a1e885d]\n  [bt] (1) /workspace/build/libtvm.so(tvm::tir::transform::PrimFuncPassNode::operator()(tv
m::IRModule, tvm::transform::PassContext const&) const+0x55b) [0x7fd90a627c7b]\n  [bt] (0) /workspace/build/libtvm.so(+0x14bc1eb) [0x7fd90af191eb]\n  File "/workspace/python/tvm/_ffi/_ctypes/packed_func.py", line 81, in cfun\n    rv = local_pyfunc(*pyargs)\n  File "/workspace/python/tvm/autotvm/measure/measure_methods.py", line 741, in verify_pass\n    raise InstantiationError("Skipped because of invalid gpu kernel")\ntvm.autotvm.task.space.InstantiationError: Skipped because of invalid gpu kernel',),), error_no=1, all_cost=0.03403472900390625, timestamp=1614703720.5951383)   [('tile_f', [-1, 32, 4, 2]), ('tile_y', [-1, 5, 1, 1]), ('tile_x', [-1, 5, 1, 1]), ('tile_rc', [-1, 32, 2]), ('tile_ry', [-1, 1, 3]), ('tile_rx', [-1, 3, 1]), ('auto_unroll_max_step', 1500), ('unroll_explicit', 0)],None,4506777

@jwfromm @csullivan @tqchen

[areusch]

@tqchen @tmoreau89 I guess this is ready for merge, TODO in original PR note notwithstanding. merging it is better than not merging it, according to the CI.