Add rocm target to topi tests (#548)

CONTRIBUTORS.md

topi/tests/python/test_topi_broadcast.py

topi/tests/python/test_topi_conv2d_hwcn.py

topi/tests/python/test_topi_conv2d_nchw.py

topi/tests/python/test_topi_dense.py

topi/tests/python/test_topi_depthwise_conv2d.py

topi/tests/python/test_topi_depthwise_conv2d_back_input.py

topi/tests/python/test_topi_depthwise_conv2d_back_weight.py

topi/tests/python/test_topi_pooling.py

topi/tests/python/test_topi_reduce.py

topi/tests/python/test_topi_relu.py

topi/tests/python/test_topi_softmax.py

topi/tests/python/test_topi_transform.py