KVM: x86: Disable KVM_INTEL_PROVE_VE by default

Disable KVM's "prove #VE" support by default, as it provides no functional
value, and even its sanity checking benefits are relatively limited.  I.e.
it should be fully opt-in even on debug kernels, especially since EPT
Violation #VE suppression appears to be buggy on some CPUs.

Opportunistically add a line in the help text to make it abundantly clear
that KVM_INTEL_PROVE_VE should never be enabled in a production
environment.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240518000430.1118488-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>