mpeg2: fix incorrect slice_vertical_position from codec layers.

mpeg2: fix incorrect slice_vertical_position from codec layers.

Correctly emit slice_vertical_position, as per the definition from
the bitstream, to the HW decoder (MFD_MPEG2_BSD_OBJECT).

Add workaround for players that have not fixed their usage of
slice_vertical_position. That field shall represent the slice vertical
position as it comes from the bitstream.

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
(cherry picked from commit 298dc939835e3080c9330b4e52e8dfac25bf3060)

Conflicts:

	NEWS