Revert "drm/exynos: g2d: fix system and runtime pm integration"

This reverts commit b05984e2.

The change, i.e. merging the sleep and runpm operations, produces
a deadlock situation:
(1) exynos_g2d_exec_ioctl() prepares a runqueue node and
    calls g2d_exec_runqueue()
(2) g2d_exec_runqueue() calls g2d_dma_start() which gets
    runtime PM sync
(3) runtime PM core calls g2d_runtime_resume()
(4) g2d_runtime_resume() calls g2d_exec_runqueue(), which
    loops back to (2)

Due to mutexes that are in place, a deadlock situation is created.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>