context: new api context_switchto() and context_perform_switch(), context_switch_to_next_guest() removed. added trap.c and sched_policy.c. schedule: new api scheduler_schedule() for default 'to next guest' behavior
context: save/restore PL1 vbar, vgic:initializes vgic state for a new guest launching. Fixes guest 1 launching failure due to invalid initial vgic/vbar states