media: venus: hfi_venus: Sanitize venus_halt_axi() per-VPU-version

Only IRIS2(_1) should enter the until-now-IS_V6() path and IRIS2_1
can be used instead of openly checking the number of VPP pipes.

Use VPU version comparison in both of these cases instead.

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>