do not use timedwait on qemu_halt_cond

do not use timedwait on qemu_halt_cond

The following conditions can cause cpu_has_work(env) to become true:

- env->queued_work_first: run_on_cpu is already kicking the VCPU

- env->stop = 1: pause_all_vcpus is already kicking the VCPU

- env->stopped = 0: resume_all_vcpus is already kicking the VCPU

- vm_running = 1: vm_start is calling resume_all_vcpus

- env->halted = 0: see previous patch

- qemu_cpu_has_work(env): when it becomes true, board code should set
  env->halted = 0 too.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>