MAINTAINERS: mark FRAMEBUFFER LAYER as Orphan

It has been a fun ride since 2017 but unfortunately I don't have
enough time to look after it properly anymore.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7b709254-9412-8473-250c-0c4e006259b3@samsung.com