st/nine: Refactor format d3d9 to pipe conversion

st/nine: Refactor format d3d9 to pipe conversion

Move the checks of whether the format is supported
into a common place.
The advantage is that allows to handle when a d3d9
format can be mapped to several formats, and that
cards don't support all of them.

Reviewed-by: Tiziano Bacocco <tizbac2@gmail.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>