doc: fix scan order specification for quantization tables.

doc: fix scan order specification for quantization tables.

Fix the VA-API specification to define all quantization tables, resp.
matrices, to be supplied in zig-zag scan order, except for the H.264
codec where scaling lists shall be provided in raster scan order.

This clarifies the existing usage inherited from the primary VA driver
implementation (Intel Poulsbo), and subsequently adopted by the major
multimedia frameworks.

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
(cherry picked from commit 835cf1ceef84cd48edddfb07bb1d2348c7b35940)