1. Five new ioctl commands of /dev/sgx are added for occlum
applications to securely get and verify DCAP quote;
2. Not all the functions of the intel DCAP package are open to
developers to simplify the DCAP usage;
3. The test may only run on the platform with DCAP driver installed;
4. A macro OCCLUM_DISABLE_DCAP is used to separate the DCAP code from
the other code.
5. Skip DCAP test when DCAP driver is not detected or in simulation mode
