fbcon: s/struct display/struct fbcon_display/

This was formerly used in fbdev drivers (not sure why, predates most
git history), but now it's entirely an fbcon internal thing. Give it a
more specific name.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Konstantin Khorenko <khorenko@virtuozzo.com>
Cc: Peter Rosin <peda@axentia.se>
Cc: Yisheng Xie <ysxie@foxmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-9-daniel.vetter@ffwll.ch