tests/exynos: add fimg2d event test

This tests async processing of G2D jobs. A separate thread is spawned
to monitor the DRM fd for events and check whether a G2D job was
completed.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Hyungwon Hwang <human.hwang@samsung.com>