clocksource: mct: extend mct to support 8 local interrupts for Exynos5420

Exynos5420 is octa-core SoC from Samsung. Hence extend exynos-mct clocksource
driver to support 8 local interrupts.

Also extend dts entries for 8 interrupts.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>