st/nine: Put ff data in a separate structure

st/nine: Put ff data in a separate structure

And make nine_state_access_transform take this
new structure as input.
Part of the refactor to move all gallium calls to
nine_state.c, and have all internal states required
for those calls in nine_context.

Signed-off-by: Axel Davy <axel.davy@ens.fr>