drm/display: Move SCDC helpers into display-helper library

SCDC is the Status and Control Data Channel for HDMI. Move the SCDC
helpers into display/ and split the header into files for core and
helpers. Update all affected drivers. No functional changes.

To avoid the proliferation of Kconfig options, SCDC is part of DRM's
support for HDMI. If necessary, a new option could make SCDC an
independent feature.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220421073108.19226-9-tzimmermann@suse.de