drm/i915: Move display device info capabilities to its own struct

This helps separate what capabilities are display capabilities.

v3: Moving display struct right after flags (Lucas)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Suggested-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181130232048.14216-2-jose.souza@intel.com