REF/PERF: PeriodEngine covers narrow type
#### Code Sample, a copy-pastable example if possible

```python
pi = pd.period_range(start=2000, end=2019, freq="A")

p = pd.Period(2010, freq="A")

In [7]: pi._engine.get_loc(p)                                                   
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-7-cd77985ba7c9> in <module>
----> 1 pi._engine.get_loc(p)

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index_class_helper.pxi in pandas._libs.index.Int64Engine._check_type()

KeyError: Period('2010', 'A-DEC')


```
#### Problem description

When i handled #28628, i found `PeriodEngine` only works for Int type. So `PeriodIndex.get_loc` compute twice because `PeriodEngine.get_loc` only accepts Int type. 


#### Suggestion
`.get_loc` on `PeriodIndex` computes once. Either expanding `PeriodEngine.get_loc` accept data type or removeing `PeriodEngine.get_loc` are ok


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

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.1.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.0.0-31-generic
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : ko_KR.UTF-8
LOCALE           : ko_KR.UTF-8

pandas           : 0.25.1
numpy            : 1.16.1
pytz             : 2018.7
dateutil         : 2.7.5
pip              : 19.3
setuptools       : 40.6.3
Cython           : 0.29.2
pytest           : 5.1.0
hypothesis       : None
sphinx           : 1.8.2
blosc            : None
feather          : None
xlsxwriter       : 1.1.2
lxml.etree       : 4.2.5
html5lib         : 1.0.1
pymysql          : 0.9.3
psycopg2         : None
jinja2           : 2.10.1
IPython          : 7.2.0
pandas_datareader: None
bs4              : 4.8.0
bottleneck       : 1.2.1
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.2.5
matplotlib       : 3.0.2
numexpr          : 2.6.8
odfpy            : None
openpyxl         : 2.5.12
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.1.0
sqlalchemy       : 1.2.15
tables           : 3.4.4
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.1.2

</details>
