drm/display: Move DSC header and helpers into display-helper module

DSC is the Display Stream Compression standard for DisplayPort. Move
the DSC code into display/ and split the header into files for protocol
core and DRM helpers. Adapt all users of the code. No functional
changes.

To avoid the proliferation of Kconfig options, DSC is part of DRM's
support for DisplayPort. If necessary, a new option could make DSC 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/20220421073108.19226-6-tzimmermann@suse.de