KVM: Documentation: Fix spec for KVM_CAP_ENABLE_CAP_VM

The documentation classifies KVM_ENABLE_CAP with KVM_CAP_ENABLE_CAP_VM
as a vcpu ioctl, which is incorrect. Fix it by specifying it as a VM
ioctl.

Fixes: e5d83c74

 ("kvm: make KVM_CAP_ENABLE_CAP_VM architecture agnostic")
Signed-off-by: Quentin Perret <qperret@google.com>
Message-Id: <20210108165349.747359-1-qperret@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>