ARM: S3C24XX: move s3c24xx_init_irq to s3c2410_init_irq

ARM: S3C24XX: move s3c24xx_init_irq to s3c2410_init_irq

The s3c24xx_init_irq function that was the base for all irq inits
is now only used to initialize the real s3c2410 irqs.

Therefore rename it and also move its declaration from plat/cpu.h
to common.h

The eint declaration is used by the vast majority of the SoCs and
gets therefore placed outside any ifdefs.

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