KVM: VMX: Shuffle support checks and hardware enabling code around

Reorder code in vmx.c so that the VMX support check helpers reside above
the hardware enabling helpers, which will allow KVM to perform support
checks during hardware enabling (in a future patch).

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-38-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>