De acordo com wiki-debian você precisa instalar o pacote xserver-xorg-video-ati
:
Edite você /etc/apt/sources.list
adicionando as non-free
sources:
deb http://httpredir.debian.org/debian/ jessie main contrib non-free
Atualize e instale o driver:
apt-get update
apt-get install firmware-linux-nonfree libgl1-mesa-dri xserver-xorg-video-ati
Reinicialize e remova o driver gráfico Intel:
Hybrid Graphics
AMD ships hybrid graphics with Intel cards . Both the cards get turned on in turn overheating the computer and it also makes lot of noise.