The new SGX Asynchronous Exit (AEX) notification mechanism (AEX-notify)
allows one enclave to receive a notification in the ERESUME after the
enclave exit due to an AEX. EDECCSSA is a new SGX user leaf function
(ENCLU[EDECCSSA]) to facilitate the AEX notification handling.
Whether the hardware supports to create enclave with AEX-notify support
is enumerated via CPUID.(EAX=0x12,ECX=0x1):EAX[10]. The new EDECCSSA
user leaf function is enumerated via CPUID.(EAX=0x12,ECX=0x0):EAX[11].
Add support to allow to expose the new SGX AEX-notify feature and the
new EDECCSSA user leaf function to KVM guest.