QEMU timer of channel 0 in i8254 is used to raise irq
at the specified moment of time. This irq can be disabled
with irq_disabled flag. But when vmstate of the pit is
loaded, timer may be rearmed despite the disabled interrupts.
This patch adds irq_disabled flag check to fix that.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Message-Id: <161537170060.6654.9430112746749476215.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>