Since commit 2bcd3eca when switching mode from X11 (ubuntu mate for
example) the display gets blurry, looking like an invalid framebuffer width.

This commit fixed atomic crtc modesetting in a totally wrong way and
introduced a local unnecessary ->enabled crtc state.

This commit reverts the crctc _begin() and _enable() changes and simply
adds drm_atomic_helper_commit_tail_rpm as helper.
Reported-by: NTony McKahan <tonymckahan@gmail.com>
Suggested-by: NDaniel Vetter <daniel@ffwll.ch>
Fixes: 2bcd3eca ("drm/meson: Fixes for drm_crtc_vblank_on/off support")
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Acked-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
[narmstrong: fixed blank line issue from checkpatch]
Link: https://patchwork.freedesktop.org/patch/msgid/20190114153118.8024-1-narmstrong@baylibre.com