KVM: Add get/set irqchip ioctls for in-kernel PIC live migration support

This patch adds two new ioctls to dump and write kernel irqchips for
save/restore and live migration. PIC s/r and l/m is implemented in this
patch.

Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Qing He <qing.he@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>