There are very few places that need to include anything from under
display/. Require the display/ prefix in #include directives, and drop
the subdirectory from the header search path.

Sort the include lists while at it.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240122101428.2683468-2-jani.nikula@intel.com