Under normal circumstances, it is impermissible to bury Muslims alongside non-Muslims. It would not be permissible to bury Muslims in a graveyard or a land where Christians, Jews, Hindus, Sikhs and people of the other faiths are buried. Similarly, it is impermissible to bury non-Muslims in a land where Muslims are buried.
This is based on the fact that since the time of the Prophet (peace be upon him), Muslims throughout the ages have been burying their dead in their own cemeteries. There have always been separate burying areas for Muslims and non-Muslims, thus the constant practice of the Muslim nation is considered to be one of the evidences.
Almighty Allah knows best.