radv: set the correct buffer size for NGG streamout

radv: set the correct buffer size for NGG streamout

If the size is passed through CmdBindTransformFeedback() uses that.

This partially fixes dEQP-VK.transform_feedback.simple.multiquery_1
by reporting the correct number of primitives written (the computation
is based on the buffer size). There is still a bug around GDS offsets
that will be fixed later.

Tested on GFX10.3 by forcing NGG streamout.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19433>