KVM: VMX: Hide VMCS control calculators in vmx.c

Now that nested VMX pulls KVM's desired VMCS controls from vmcs01 instead
of re-calculating on the fly, bury the helpers that do the calcluations
in vmx.c.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210810171952.2758100-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>