drm: Move drm_crtc_init from drm_crtc.h to drm_plane_helper.h

Just a bit of OCD cleanup on headers - this function isn't the core
interface any more but just a helper for drivers who haven't yet
transitioned to universal planes. Put the declaration at the right
spot and sprinkle necessary #includes over all drivers.

Maybe this helps to encourage driver maintainers to do the switch.

v2: Fix #include ordering for tegra, reported by 0-day builder.

v3: Include required headers, reported by Thierry.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Thierry Reding <treding@nvidia.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/tegra/dc.c

@@ -15,6 +15,8 @@
 #include "drm.h"
 #include "gem.h"
 
+#include <drm/drm_plane_helper.h>
+
 struct tegra_dc_soc_info {
 	bool supports_interlacing;
 	bool supports_cursor;