kvmvapic: fix migration when VM paused and when not running Windows

kvmvapic: fix migration when VM paused and when not running Windows

This patch fixes migration by extending do_vapic_enable function. This function
called vapic_enable which read cpu number from the guest memory. When cpu
number could not be read, vapic was not enabled while loading the VM state.
This patch adds required code for cpu_number=0 to do_vapic_enable function,
because it is called only when cpu_number=0.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>