Revert "drm/exynos/decon5433: implement frame counter"

This reverts commit 0586feba

This patch makes it to need get_vblank_counter callback in crtc
to get frame counter from decon driver.

However, drm_dev->max_vblank_count is a member unique to
vendor's DRM driver but in case of ARM DRM, some CRTC devices
don't provide the frame counter value. As a result, this patch
made extension and clone mode not working.

Instead of this patch, we may need separated max_vblank_count
which belongs to each CRTC device, or need to implement frame
counter emulation for them who don't support HW frame counter.

Signed-off-by: Inki Dae <inki.dae@samsung.com>