Revert "drm/radeon: rework page flip handling v3"

This reverts commit 1aab5514ca9604e0263f658a067da0189c86a35b.

Apply the fixed up version instead.

diff --cc drivers/gpu/drm/radeon/radeon.h
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_display.c
Simple merge

diff --cc drivers/gpu/drm/radeon/radeon_mode.h
Simple merge