Bring up AP of VMX domain.

Bring up AP of VMX domain.
1) add INIT-SIPI-SIPI IPI sequence handling code to HVM virtual lapic
code.
2) add an new interface init_ap_context to hvm_funcs, and implement the
VMX side.
3) add a hvm generic function hvm_bringup_ap, which in turn calls
init_ap_context.

Signed-off-by: Xin Li <xin.b.li@intel.com>
Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>