ARM: EXYNOS4: Add chained enrty/exit function to uart interrupt handler

This patch adds chained IRQ enter/exit functions to uart
interrupt handler in order to function correctly on primary
controllers with different methods of flow control.

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