ARM: EXYNOS: Remove legacy interrupt initialization code

This patch removes legacy IRQ initialization code that was used to set
up interrupt handling when booting with ATAGS, which is not supported
any more.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>