exynos: fimc-is: Internal buffer list cleanup

exynos: fimc-is: Internal buffer list cleanup

As the driver maintaines separate buffer lists per each
video device which are beyond control of v4l2/vb2
framework, those lists should be properly handled
and cleared once the buffers are no longer
available. The changes introduced allow controlling
state of each queued buffer and removing it from
internal buffer lists when needed.

Signed-off-by: Beata Michalska <b.michalska@samsung.com>
Change-Id: I4dea7df3910d6836edee1387c5a1147649043b81