hv: make init_vmcs as a event of VCPU

After changing init_vmcs to smp call approach and do it before
launch_vcpu, it could work with noop scheduler. On real sharing
scheudler, it has problem.

   pcpu0                  pcpu1            pcpu1
 vmBvcpu0                vmAvcpu1         vmBvcpu1
                         vmentry
init_vmcs(vmBvcpu1) vmexit->do_init_vmcs
                    corrupt current vmcs
                        vmentry fail
launch_vcpu(vmBvcpu1)

This patch mark a event flag when request vmcs init for specific vcpu. When
it is running and checking pending events, will do init_vmcs firstly.

Tracked-On: #4178
Signed-off-by: Shuo A Liu <shuo.a.liu@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/include/arch/x86/guest/vcpu.h

@@ -86,6 +86,11 @@
  */
 #define ACRN_REQUEST_VPID_FLUSH			7U
 
+/**
+ * @brief Request for initilizing VMCS
+ */
+#define ACRN_REQUEST_INIT_VMCS			8U
+
 /**
  * @}
  */