drm/rockchip: vop: no need wait vblank on crtc enable

Since atomic framework, crtc enable and disable are in pairs,
no need to wait vblank.

Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Reviewed-by: Sandy huang <sandy.huang@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1501494577-6884-1-git-send-email-mark.yao@rock-chips.com