frontends/va: Alloc interlaced surface for interlaced pics

frontends/va: Alloc interlaced surface for interlaced pics

When decoding interlaced pics, the output surface should
also be allocated as interlaced to make the deinterlace
postproc filter work correctly.

This makes deinterlacing work for drivers that supports, but
not prefers, interlaced surfaces.

Use extra buffer instead of reallocating as non-interlaced
when exporting interlaced surfaces.

v2: Avoid reallocating in vlVaExportSurfaceHandle

Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24361>