KVM: VMX: Add emulation of SGX Launch Control LE hash MSRs

Emulate the four Launch Enclave public key hash MSRs (LE hash MSRs) that
exist on CPUs that support SGX Launch Control (LC).  SGX LC modifies the
behavior of ENCLS[EINIT] to use the LE hash MSRs when verifying the key
used to sign an enclave.  On CPUs without LC support, the LE hash is
hardwired into the CPU to an Intel controlled key (the Intel key is also
the reset value of the LE hash MSRs). Track the guest's desired hash so
that a future patch can stuff the hash into the hardware MSRs when
executing EINIT on behalf of the guest, when those MSRs are writable in
host.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Message-Id: <c58ef601ddf88f3a113add837969533099b1364a.1618196135.git.kai.huang@intel.com>
[Add a comment regarding the MSRs being available until SGX is locked.
 - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>