dt-bindings: exynos5433-decon: add TE interrupt binding

DECON command mode can use hardware trigger where transmission
is triggered automatically, or software trigger - where TE interrupt
handler should trigger transmission.
DECON will use software trigger if TE interrupt is specified.

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