ARM: EXYNOS: Fix compilation error when CONFIG_OF is not defined

Fixed following compile time error.
arch/arm/mach-exynos/common.c: In function 'exynos5_init_irq':
arch/arm/mach-exynos/common.c:539:2: error: implicit declaration of function 'of_irq_init'
arch/arm/mach-exynos/common.c:539:14: error: 'exynos4_dt_irq_match' undeclared (first use in this function)
arch/arm/mach-exynos/common.c:539:14: note: each undeclared identifier is reported only once for each function it appears in

Cc: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>