Add loongarch support

[212dandan]

This commit is for a new architecture--loongarch.

Compilation and installation are normal in the loongarch architecture.
Tests unit test passed in pyroute2 project.
Examples,
First,loongarch architecture displays.
loongson@loongson-pc:~/dd/python-pyroute2$ lscpu | grep Architecture
Architecture: loongarch64

Second,tests unit test passed in pyroute2 project.
loongson@loongson-pc:~/dd/python-pyroute2$ python3.7 -m nose -v tests/unit
test_common.TestAddrPool.test_alloc_aligned ... ok
test_common.TestAddrPool.test_alloc_odd ... ok
test_common.TestAddrPool.test_free ... ok
test_common.TestAddrPool.test_free_fail ... ok
test_common.TestAddrPool.test_free_reverse_fail ... ok
test_common.TestAddrPool.test_locate ... ok
test_common.TestAddrPool.test_reverse ... ok
test_common.TestAddrPool.test_setaddr_allocated ... ok
test_common.TestAddrPool.test_setaddr_free ... ok
test_common.TestCommon.test_dqn2int ... ok
test_common.TestCommon.test_hexdump ... ok
test_common.TestCommon.test_uifname ... ok
test_common.TestCommon.test_uuid32 ... ok
Ran 13 tests in 0.247s
OK

Third,users test passed in the loongarch architecture.
Users test some netns:: interfaces those also pass, such as
loongson@loongson-pc:~/dd/python-pyroute2$ sudo python3
Python 3.7.3 (default, Sep 12 2020, 09:01:12)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

import pyroute2
from pyroute2 import NetNS
from pprint import pprint
ns = NetNS('test')
pprint(ns.get_links())
[{'__align': (),
'attrs': [('IFLA_IFNAME', 'lo'),
('IFLA_TXQLEN', 1000),
......
ns.close()

loongson@loongson-pc:~/dd/python-pyroute2$ sudo python3
Python 3.7.3 (default, Sep 12 2020, 09:01:12)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

from pyroute2 import netns
netns.create('test')
print(netns.listnetns())
['test', 'aaaaaa']
netns.remove('test')

The end, we look forward to your reply and we hope this submission could be merged.
Thanks.