drm/rockchip: convert to helper nonblocking atomic commit

With the various bits fixed rockchip now has an atomic compliant
handling/signalling of crtc_state->event, which means we can just
switch over to the new nonblocking helpers and remove some code.

v2: Fixes from Tomeu.

v3: Send out vblank events correctly when shutting down a crtc for
good. This is part of the atomic interface contract.

v4: Properly protect vop->event.

v5: Add more WARN_ON to check vop->event isn't clobbered.

Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Mark yao <mark.yao@rock-chips.com>
Tested-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>