According to the definition of tribe, Zimbabwe only has one African tribe- the Bantu.
'A tribe is a unit of sociopolitical organization consisting of a number of families, clans, or other groups who share a common ancestry and culture and among whom leadership is typically neither formalized nor permanent' (thefreedictionary.com).
All Bantu Africans share a common ancestry i.e. all originated from ancient Egypt. They were also called Kushites by Arab adventurous who were the 1st to venture into Africa along the East Coast. Ancient Egyptians originated from Nubia (Ethiopia) that is why to this day Ethiopians say that Egypt is one of their colonies. All ancient chronicles refer to Negroes as Ethiopians (Greek, Roman, and Arab chronicles). The word Bantu was 1st used by Earl Grey in 1857 after noting common traits in African languages especially persistence of the root -ntu.
So in essence, there is only one tribe in Africa- The Ethiopian, also known as Kushite, also known as Bantu.