Use `keepdims` and maintain backward compatible for `keep_dims` (#12756)

* Use `keepdims` and maintain backward compatible for `keep_dims`

This fix tries to address the issue raised in 6815 where
both `keepdims` and `keep_dims` were used with inconsistency.

This fix changes related api to `keepdims` while at the same
time maintain backward compatible for `keep_dims` so that
use will not be impacted.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Use `@deprecated_args`

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update goldens API for compatibility changes

This commit updates goldens API:
```
bazel-bin/tensorflow/tools/api/tests/api_compatibility_test \
          --update_goldens True
```

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>