Okay, So I ran into some troubles with the disk and I had lost all setup. So had to start from begining, starting from creating the opt partition. Below is the command log that is specific to HA.
opkg install gcc
opkg install busybox ldd make gawk sed
opkg install coreutils-install
wget -qO- http://pkg.entware.net/binaries/armv7/include/include.tar.gz | tar xvz -C /opt/include
opkg install python3
opkg install python3-pip
python3 -m pip install --upgrade pip setuptools
mkdir /opt/pip_home
source /opt/bin/gcc_env.sh
cd /opt/lib
ln -s libffi.so.6 libffi.so
opkg install python-dev
opkg install python3-dev
HOME=/opt/pip_home pip3 install homeassistant
…
After long wait time, all packages are compiled and installed including cffi.
Installing collected packages: voluptuous, voluptuous-serialize, ruamel.yaml, Unidecode, python-slugify, attrs, multidict, idna, yarl, chardet, async-timeout, aiohttp, certifi, MarkupSafe, jinja2, pyyaml, pytz, astral, urllib3, requests, asn1crypto, six, pycparser, cffi, cryptography, PyJWT, bcrypt, homeassistant
Running setup.py install for voluptuous-serialize ... done
Running setup.py install for ruamel.yaml ... done
Running setup.py install for python-slugify ... done
Running setup.py install for multidict ... done
Running setup.py install for yarl ... done
Running setup.py install for MarkupSafe ... done
Running setup.py install for pyyaml ... done
Running setup.py install for pycparser ... done
Running setup.py install for cffi ... done
Successfully installed MarkupSafe-1.1.1 PyJWT-1.6.4 Unidecode-1.0.23 aiohttp-3.5.4 asn1crypto-0.24.0 astral-1.10.1 async-timeout-3.0.1 attrs-18.2.0 bcrypt-3.1.6 certifi-2019.3.9 cffi-1.12.2 chardet-3.0.4 cryptography-2.5 homeassistant-0.90.1 idna-2.8 jinja2-2.10 multidict-4.5.2 pycparser-2.19 python-slugify-1.2.6 pytz-2018.9 pyyaml-3.13 requests-2.21.0 ruamel.yaml-0.15.88 six-1.12.0 urllib3-1.24.1 voluptuous-0.11.5 voluptuous-serialize-2.1.0 yarl-1.3.0