drm: Remove unnecessary include statements of drm_plane_helper.h

Remove the include statement for drm_plane_helper.h from all the files
that don't need it. Althogh the header file is almost empty, many drivers
include it somewhere.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220720083058.15371-5-tzimmermann@suse.de