drm/exynos/decon5433: set STANDALONE_UPDATE_F also if planes are disabled

STANDALONE_UPDATE_F should be set if something changed in plane configurations,
including plane disable.
The patch fixes page-faults bugs, caused by decon still using framebuffers
of disabled planes.

v2: fixed clear-bit code (Thx Marek)
v3: use test_and_clear_bit (Thx Joonyoung)

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Tested-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>