ARM: S3C24XX: create dedicated irq init functions for s3c2440 and s3c2442

s3c2440 and s3c2442 need separate init functions, as the s3c2440 contains
even more differing irqs that will be moved in the following patch.

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