KVM: s390: Clear valid_wakeup in kvm_s390_handle_wait(), not in arch hook

Move the clearing of valid_wakeup from kvm_arch_vcpu_block_finish() so
that a future patch can drop said arch hook.  Unlike the other blocking-
related arch hooks, vcpu_blocking/unblocking(), vcpu_block_finish() needs
to be called even if the KVM doesn't actually block the vCPU.  This will
allow future patches to differentiate between truly blocking the vCPU and
emulating a halt condition without introducing a contradiction.

Alternatively, the hook could be renamed to kvm_arch_vcpu_halt_finish(),
but there's literally one call site in s390, and future cleanup can also
be done to handle valid_wakeup fully within kvm_s390_handle_wait() and
allow generic KVM to drop vcpu_valid_wakeup().

No functional change intended.

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>