i965/vs: Rework memory contexts for shader compilation data.

i965/vs: Rework memory contexts for shader compilation data.

During compilation, we allocate a bunch of things: the IR needs to last
at least until code generation...and then the program store needs to
last until after we upload the program.

For simplicity's sake, just keep it all around until we upload the
program.  After that, it can all be freed.

This will also save a lot of headaches during the upcoming refactoring.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>