ARM: EXYNOS4: Add irq definition for kernel global timer

This patch adds IRQ_MCT_G0 to irq map. IRQ_MCT_G0 is an interrupt
of MCT comparator and used for kernel global timer.

Signed-off-by: Changhwan Youn <chaos.youn@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>