fbdev/sh_mobile: remove sh_mobile_lcdc_display_notify

It's dead code, and removing it avoids me having to understand
what it's doing with lock_fb_info.

v2: Also remove sh_mobile_lcdc_must_reconfigure, now unused (Sam).

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be> (v1)
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-12-daniel.vetter@ffwll.ch