target/i386: Add SGX aex-notify and EDECCSSA support

target/i386: Add SGX aex-notify and EDECCSSA support

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.

Link: https://lore.kernel.org/lkml/166760360549.4906.809756297092548496.tip-bot2@tip-bot2/
Link: https://lore.kernel.org/lkml/166760360934.4906.2427175408052308969.tip-bot2@tip-bot2/
Reviewed-by: Yang Zhong <yang.zhong@linux.intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Message-Id: <20221109024834.172705-1-kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>