drm/exynos/decon5433: kill BIT_WIN_UPDATED flag

The flag was used to trigger software update in TE IRQ handler only
if framebuffers were replaced. Since TE update is triggered always
when VBLANKs are enabled and after framebuffer replacement VBLANKs
are always enabled the flag becomes redundant.

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