BUG: ExtensionArray with 2D datetime64 values errors on display formatting
- [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.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

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

```python
import numpy as np
import pandas as pd
import pandas.io.formats.format as fmt
x = pd.date_range('2018-01-01', periods=5, freq='H').to_numpy()
x = np.tile(x, (3, 1))
formatter = fmt.Datetime64Formatter(x)
result = formatter.get_result()
```

#### Problem description

When using a Pandas ExtensionArray that has 2D values of Datetime64 dtype, Pandas errors on formatting the values with the following:
```
File "/ib/python3.8/site-packages/pandas/io/formats/printing.py", line 73, in <listcomp>
    return [x.rjust(max_len) for x in texts]
AttributeError: 'list' object has no attribute 'rjust'
```

The above is also true when using the `Datetime64Formatter` directly with values of ndim > 1.

#### Expected Output
Formatting that takes into account dimensionality:
```
[' [2018-01-01 00:00:00, 2018-01-01 01:00:00, 201...', ' [2018-01-01 05:00:00, 2018-01-01 06:00:00, 201...']
```


#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : db08276bc116c438d3fdee492026f8223584c477
python           : 3.8.6.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.0-54-generic
Version          : #60-Ubuntu SMP Fri Nov 6 10:37:59 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.3
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.3
setuptools       : 49.6.0.post20201009
Cython           : None
pytest           : 6.1.1
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.18.1
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.2
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 1.0.1
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.2
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
