drm/exynos: Remove non-DT support in exynos_hdmi

Since commit 383ffda2 ("ARM: EXYNOS: no more support non-DT
for EXYNOS SoCs"), Exynos platform is DT only. Hence remove
all the conditional macros and make the driver DT only.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>