KVM x86 Xen changes for 6.7:

 - Omit "struct kvm_vcpu_xen" entirely when CONFIG_KVM_XEN=n.

 - Use the fast path directly from the timer callback when delivering Xen timer
   events.  Avoid the problematic races with using the fast path by ensuring
   the hrtimer isn't running when (re)starting the timer or saving the timer
   information (for userspace).

 - Follow the lead of upstream Xen and ignore the VCPU_SSHOTTMR_future flag.