lavc/vaapi_av1: Avoid sending the same slice buffer multiple times

lavc/vaapi_av1: Avoid sending the same slice buffer multiple times

When there are multiple tiles in one slice buffer, use multiple slice
params to avoid sending the same slice buffer multiple times and thus
increasing the bitstream size the driver will need to upload to hw.

Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Signed-off-by: David Rosca <nowrep@gmail.com>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
(cherry picked from commit d2d911eb9a2fc6eb8d86b3ae025a56c1a2692fba)

Gbp-Pq: Name 0002-lavc-vaapi_av1-Avoid-sending-the-same-slice-buffer-m.patch