Add oneDNN support for reduce operators

[bgawrych]

Description

Add oneDNN support for reduction operators: sum and mean, for both nd and np interfaces

[mxnet-bot]

Hey @bgawrych , Thanks for submitting the PR
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[bartekkuncer]

Overall looks good. Only some cosmetic changes.

[bgawrych]

@mxnet-bot run ci [miscellaneous, windows-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [miscellaneous, windows-gpu]

[bgawrych]

Perf results on CLX8280 (28 cores):

Script:

import mxnet
import mxnet.gluon.nn as nn
import mxnet.numpy as np
import time

dims = [128, 512, 1024, 4096]
print("shape;axis;time;mean")
for ndim in range (2):
   for dim1 in dims:
     for dim2 in dims:
        shape = (dim1, dim2) if ndim == 0 else (32, dim1, dim2)
        a = np.random.uniform(-1.0, 1.0, shape).astype(np.float32)
        for axis in range(2 + ndim):
            tic = time.time()
            for i in range(100):
                out = np.mean(a, axis=axis)
                out.wait_to_read()
            toc = time.time()
            print(f"{shape};{axis};{toc-tic}")

[bgawrych]

Merging, @szha if there is any procedure of merging own commits let me know