va: vp9dec: update segmentation and store the result.

va: vp9dec: update segmentation and store the result.

The segmentation is stateful, its information may depend on the previous
segmentation setting. For example, if loop_filter_delta_enabled is TRUE,
the filter_level[GST_VP9_REF_FRAME_INTRA][1] should inherit the previous
frame's value and can not be calculated by the current frame's segmentation
data only. So we need to maintain the segmentation state inside the vp9
decoder and update it when the new frame header comes.

We also fix the CLAMP issue of lvl_seg and intra_lvl because of their wrong
uint type here.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2369>