media: venus: core: Assign registers based on VPU version

The current assumption of IS_V6 is overgeneralized. Adjust the logic
to take the VPU hardware version into account.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>