KVM: x86: Clear pv_unhalted on all transitions to KVM_MP_STATE_RUNNABLE

KVM: x86: Clear pv_unhalted on all transitions to KVM_MP_STATE_RUNNABLE

In kvm_set_mp_state(), ensure that vcpu->arch.pv.pv_unhalted is always
cleared on a transition to KVM_MP_STATE_RUNNABLE, so that the next HLT
instruction will be respected.

Fixes: 6aef266c6e17 ("kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks")
Fixes: b6b8a1451fc4 ("KVM: nVMX: Rework interception of IRQs and NMIs")
Fixes: 38c0b192bd6d ("KVM: SVM: leave halted state on vmexit")
Fixes: 1a65105a5aba ("KVM: x86/xen: handle PV spinlocks slowpath")
Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20250113200150.487409-3-jmattson@google.com
[sean: add Xen PV spinlocks to the list of Fixes, tweak changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>