drm/exynos: decon: clean up interface type

This patch cleans up interface type relevant codes.

Trigger mode is determinded only by i80 mode, which isn't
related to Display types - HDMI or Display controller.
So this patch makes the trigger mode to be set only in case of
i80 mode - For DECON-TV, HW Trigger mode is flaged mandatorily
because HDMI Timing Generator generates VSYNC signal
which works as a hardware trigger.

Changelog v2.
- If interface type is HDMI then set out_type to I80.
- fix compile warning.

Signed-off-by: Inki Dae <inki.dae@samsung.com>