Support for fp16 in SpM x DnsM on GPU

[access2rohit]

Description

enables fp16 DType suport in following case

dot(csr, dense1) = dense2 and dot(csr.T, dense1) = dense2

Will add test case shortly

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Testing

pytest) ubuntu@ip-172-31-90-243 ~/workspace/incubator-mxnet (spgemm_fp16) $ python -m pytest -s --exitfirst --verbose tests/python/gpu/test_operator_gpu.py::test_fp16_spmm
=============================================================================================== test session starts ===============================================================================================
platform linux -- Python 3.6.10, pytest-5.3.5, py-1.8.2, pluggy-0.13.1 -- /home/ubuntu/anaconda3/envs/pytest/bin/python
cachedir: .pytest_cache
rootdir: /home/ubuntu/workspace/incubator-mxnet, inifile: pytest.ini
collected 1 item

tests/python/gpu/test_operator_gpu.py::test_fp16_spmm [09:52:41] ../src/base.cc:84: Upgrade advisory: this mxnet has been built against cuDNN lib version 7501, which is older than the oldest version tested by CI (7600).  Set MXNET_CUDNN_LIB_CHECKING=0 to quiet this warning.
[09:52:43] ../src/storage/storage.cc:198: Using Pooled (Naive) StorageManager for GPU
PASSED

[mxnet-bot]

Hey @access2rohit , Thanks for submitting the PR
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[access2rohit]

@mxnet-label-bot add [pr-work-in-progress]

[access2rohit]

@ptrendx Can you take an initial look ? I am yet to add test case though

[ptrendx]

Looks good :-)

[access2rohit]

@mxnet-label-bot update [pr-awaiting-review]

[access2rohit]

@ptrendx I have added test case. Can you help with review and merge

[sandeep-krishnamurthy]

Merging per previous review by @ptrendx