KVM: x86: Force kvm_rebooting=true during emergency reboot/crash

Set kvm_rebooting when virtualization is disabled in an emergency so that
KVM eats faults on virtualization instructions even if kvm_reboot() isn't
reached.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-18-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>