ilo: add a new struct for context states

ilo: add a new struct for context states

Move pipe states in ilo_context to the new ilo_state_vector.  The motivation
is that ilo_context consists of several loosely related things.  When we need
an ilo_context somewhere, we usually need only one or two of the things in it.
This change makes ilo_state_vector one such thing.

An immediate result is that we no longer need ilo_context in 3D pipelines,
something we have planned for since early days.