media: mtk-vpu: VPU should be in idle state before system is suspended

VPU should be in idle state before system is suspended
or it will work abnormally like VPU program counter not
in a correct address or VPU reset

Signed-off-by: Irui Wang <irui.wang@mediatek.com>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>