irqchip: Andestech Internal Vector Interrupt Controller driver

This patch adds the Andestech Internal Vector Interrupt Controller
driver. You can find the spec here. Ch4.9 of AndeStar SPA V3 Manual.
http://www.andestech.com/product.php?cls=9

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>