In Hinduism, Near Burial Grounds have lord Shiva paintings but people shout "Govinda Govinda" for death rites. Both are different gods, then why lord Venkateshwar paintings are not present at burial grounds?
Your question can be divided into two different questions.
Why are there pictures of Shiva painted near cremation walls?
Why do people chant Govinda Govinda during death rites?
Now answering your first question
1. Why are there pictures of Shiva painted near cremation walls?
Lord Shiva is called as Bhootanath meaning the lord of Ghosts. He is accompanied by many ghosts. His ganas(forces) consist of different types of Ghosts.
Lord Shiva is seated in a crematorium.
O thou of sweet smiles, the multitudes of ghostly beings that are my companions love to reside in such spots. I do not like, O goddess, to reside anywhere without those ghostly creatures being by my side. Hence, the crematorium is a sacred abode to me. Indeed, O auspicious lady, it seems to me to be the very heaven. Highly sacred and possessed of great merit, the crematorium is much applauded by persons desirous of having holy abodes.' [Anushasana Parva section CXLI]
All friends and family members weep for sometime for the person who had passed away. Bury or cremate the body of the deceased one and leave. But it is a symbolism to show that he is the only one who cares after the death of a person too. So he resides in a crematorium. So, his paintings are depicted in a crematorium.
2.Why do people chant "Govinda Govinda" during death rites?
In Hinduism, optimistic attitude is encouraged rather than pessimistic. If we observe, people say His/her soul is united with Shiva(Shivaikyam) or He has reached Vaikuntham while conveying a person's death message to others i.e., We do not try to speak bad or inauspicious talk even at the time of inauspicious events. We can find many similar statements in different languages and regions of India.
A person's death is an inauspicious event. But in Hinduism, is seen as a way to attain salvation. So, people take the name of the Lord while sending a person to the abode of Lord. The chant you say is taken in Telugu states. In North Indian states, it is राम नाम सत्य है Rām nām Satya hai meaning the name of the Rama is the truth.
So, people take the name of Govinda indicating that the person has attained the Lord's abode.