drm/exynos/decon5433: configure sysreg in case of hardware trigger

In case of HW trigger mode, sysreg register should be configured to
enable TE functionality. The patch refactors also trigger setup function.

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