drm/exynos: scaler: Reset hardware before starting the operation

Ensure that Scaler hardware is properly reset and interrupts are cleared
before processing next image.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>