media: mtk-vcodec: reset segment data then trig decoder

VP9 bitstream specification indicate segment data should reset to
default when meet key frames, intra only frames or enable error
resilience mode. So memset segmentation map buffer before every
decode process is not appropriate.

Reset segment data only when needed, then start decoder hardware

Signed-off-by: Rui Wang <gtk_ruiwang@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>