use struct sched_object as the main interface of scheduling, then
make scheduler as an independent module to vcpu:
- add struct sched_object as one field in struct vcpu
- define sched_object.thread for switch_to thread
- define sched_object.prepare_switch_out/in for prepare_switch before
switch_to
- move context_switch_out/context_switch_in into vcpu.c as
vcpu.sched_obj.prepare_switch_out/in
- make default_idle as global idle.thread for idle_thread
- make vcpu_thread as vcpu.sched_obj.thread for each vcpu thread
- simplify switch_to based on sched_object
Tracked-On: #1842
Signed-off-by: Jason Chen CJ <jason.cj.chen@intel.com>
Acked-by: Eddie Dong <edide.dong@intel.com>