sgx: Add mandatory id field to SgxEpcConfig

In order to uniquely identify each SGX EPC section, we introduce a
mandatory option `id` to the `--sgx-epc` parameter.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/api/openapi/cloud-hypervisor.yaml

@@ -851,9 +851,12 @@ components:
 
     SgxEpcConfig:
       required:
+      - id
       - size
       type: object
       properties:
+        id:
+          type: string
         size:
           type: integer
           format: int64