KVM: Bypass irq_pending get/set when using in kernel irqchip

vcpu->irq_pending is saved in get/set_sreg IOCTL, but when in-kernel
local APIC is used, doing this may occasionally overwrite vcpu->apic to
an invalid value, as in the vm restore path.

Signed-off-by: Qing He <qing.he@intel.com>