i965/vs: Move struct brw_compile (p) entirely inside vec4_generator.

i965/vs: Move struct brw_compile (p) entirely inside vec4_generator.

The brw_compile structure contains the brw_instruction store and the
brw_eu_emit.c state tracking fields.  These are only useful for the
final assembly generation pass; the earlier compilation stages doesn't
need them.

This also means that the code generator for future hardware won't have
access to the brw_compile structure, which is extremely desirable
because it prevents accidental generation of Gen4-7 code.

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