KVM: VMX: Make VMCS configuration/capabilities structs read-only after init

Tag vmcs_config and vmx_capability structs as __init, the canonical
configuration is generated during hardware_setup() and must never be
modified after that point.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-31-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>