i965/fs: Expose "urb_setup" as part of brw_wm_prog_data.

i965/fs: Expose "urb_setup" as part of brw_wm_prog_data.

At the moment, for Gen6+, the FS assumes that all varying inputs are
delivered to it in the order in which they appear in the
gl_program::InputsRead bitfield, and the SF/SBE setup code ensures
that they are delivered in this order.

When we add support for more than 64 varying components, this will no
longer always be possible, because the Gen6+ SF/SBE stage is only
capable of performing arbitrary reorderings of 16 varying slots.

To allow extra flexibility in the ordering of FS varyings, this patch
causes the FS to advertise exactly what ordering it expects.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>