[libvirt] New Feature: Identify Intel SGX support

Hello Team, Greetings! We want to identify if the platform is Intel Software Guard Extensions<https://software.intel.com/en-us/sgx> (SGX) capable. The management platform (ex. Openstack) can use this information to launch VM that can run secure application code and data. Intel(r) SGX offers hardware-based memory encryption that isolates specific application code and data in memory. Regards, Larkins Carvalho Intel Corp.