BUG: Load ORC-format data failed when pandas version>1.2.0.dev0
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [x] (optional) I have confirmed this bug exists on the master branch of pandas.
https://github.com/pandas-dev/pandas/blob/master/pandas/io/orc.py#L15-L54

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#### Code Sample, a copy-pastable example

```python
...
import pandas as pd
orc_data = pd.read_orc(orc_file_path)
```

#### Problem description

Pandas uses [PyArrow](https://arrow.apache.org/docs/python) package to load ORC/Parquet data. 

For the orc data format, it will use `pyarrow.orc.ORCFile` to read data ([orc.py](https://github.com/pandas-dev/pandas/blob/master/pandas/io/orc.py#L53)), but the PyArrow does not declare `orc` in [\_\_init\_\_.py](https://github.com/apache/arrow/blob/master/python/pyarrow/__init__.py) file, so pandas will raise an AttributeError: module 'pyarrow' has no attribute 'orc'

![image](https://user-images.githubusercontent.com/16681550/114521032-9da66800-9c74-11eb-8f03-11865f111be9.png)

This bug will occur if the Pandas version is greater than v1.2.0.dev0(after [commit-6d1541e](https://github.com/pandas-dev/pandas/commit/6d1541e1782a7b94797d5432922e64a97934cfa4)). Before that, `pandas/io/orc.py` will declare `import pyarrow.orc` before uses pyarrow to load orc data([v1.1.5/pandas/io.orc.py/](https://github.com/pandas-dev/pandas/blob/v1.1.5/pandas/io/orc.py#L51)).

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Testing environment:

- Ubuntu 18.04
- python 3.7
- pandas v1.2.1
- pyarrow v3.0.0 (install via pip)(I haven't installed pyarrow via Conda for testing yet.)