hv: implement NEED_SHUTDOWN_VM request to idle thread

For pre-launched VMs and SOS, VM shutdown should not be executed in the
current VM context.

- implement NEED_SHUTDOWN_VM request so that the BSP of the target VM can shut
  down the guest in idle thread.
- implement shutdown_vm_from_idle() to shut down target VM.

Tracked-On: #2700
Signed-off-by: Zide Chen <zide.chen@intel.com>
Signed-off-by: Sainath Grandhi <sainath.grandhi@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/Makefile

@@ -213,6 +213,7 @@ C_SRCS += arch/x86/guest/vmcs.c
 C_SRCS += arch/x86/guest/vmexit.c
 S_SRCS += arch/x86/guest/vmx_asm.S
 C_SRCS += arch/x86/guest/trusty.c
+C_SRCS += arch/x86/guest/vm_reset.c
 C_SRCS += arch/x86/cat.c
 C_SRCS += arch/x86/lib/memory.c
 C_SRCS += lib/string.c