irqchip: s3c24xx: make interrupt handling independent of irq_domain structure

Keep a pointer to the corresponding s3c_irq_data struct as irq_chip_data.
This removes the need to fetch the intc struct from the irq_domains
host_data, thus making it independent of the underlying irq_domain
structure.

Also keep the real register offset of the interrupt in the s3c_irq_data
struct to make it independent of the hwirq structure in the irq_domain

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>