drm/exynos: fix interlace resolutions for exynos5420

Modified code for calculating hdmi IP register values from drm timing
values. The modification is based on the inputs from hw team and specifically
proposed for 1440x576i and 1440x480i. But same changes holds good for other
interlaced resolutions also.

Signed-off-by: Rahul Sharma <rahul.sharma@samsung.com>
Acked-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>