Move vcpu API create_vcpu to common.
* Break create_vcpu into common vcpu init and arch_init_vcpu
for arch-specific initialization.
* Move vcpu_thread to arch-specific and rename to arch_vcpu_thread
Tracked-On: #8830
Signed-off-by: Yifan Liu <yifan1.liu@intel.com>
Reviewed-by: Fei Li <fei1.li@intel.com>
Acked-by: Wang Yu1 <yu1.wang@intel.com>