ARM: S3C24XX: transform irq handling into a declarative form

The irqs available on the machine and even the bit settings in the
irq registers differ a lot through all the s3c24xx subarchitectures.
This results in each subarch having its own irq init which adds its
specific irqs to the base ones created in plat-s3c24xx/irq.c.

This of course makes a future move to devicetree hard to implement.

Therefore this patch transforms the base irq handling to a declarative
style, where the irq types as well as its parent/child relationship
gets read from a predefined datastructure, which later on can hopefully
be easily represented in devicetree too.

It should also be easy to include the subarch specific irqs here
in later patches, reducing code size and duplication.

It should not affect anything outside of the file, as the original
irq numbers and their handling are preserved (hopefully) correctly.

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