fbdev/sh_mob: Remove fb notifier callback

This seems to be entirely defunct:

- The FB_EVEN_SUSPEND/RESUME events are only sent out by
  fb_set_suspend. Which is supposed to be called by drivers in their
  suspend/resume hooks, and not itself call into drivers. Luckily
  sh_mob doesn't call fb_set_suspend, so this seems to do nothing
  useful.

- The notify hook calls sh_mobile_fb_reconfig() which in turn can
  call into the fb notifier. Or attempt too, since that would
  deadlock.

So looks like leftover hacks from when this was originally introduced
in

commit 6011bdea
Author: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Date:   Wed Jul 21 10:13:21 2010 +0000

    fbdev: sh-mobile: HDMI support for SH-Mobile SoCs

So let's just remove it.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Markus Elfring <elfring@users.sourceforge.net>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-21-daniel.vetter@ffwll.ch