drm/exynos/hdmi: improve HDMI/ACR related code

Simple formula can be used to calculate CTS and N coefficients.
Additionaly ACR registers have different offsets for different versions
of IP.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>