drm/panel: Do not include <linux/fb.h>

Remove unnecessary include statements for <linux/fb.h>. No functional
changes. Include <linux/of.h> where the driver got the header file via
<linux/fb.h>.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20230111130206.29974-6-tzimmermann@suse.de