Create a new wrapper function for this, feels like there's some
refactoring room here between the two modes.

v2: backlight notifier is also interested in the mode change event,
it calls lcd->set_mode, of which there are 3 implementations. Thanks
to Maarten for spotting this. So we keep that. We can ditch the differentiation
between mode change and all mode changes (because backlight notifier
doesn't care), and we can drop the FBINFO_MISC_USEREVENT stuff too,
because that's just to prevent recursion between fbmem.c and fbcon.c.

While at it flatten the control flow a bit.

v3: Need to add a static inline to the dummy function.

v4: Add missing #include <fbcon.h> to sh_mob (Sam).

Cc: Sam Ravnborg <sam@ravnborg.org>
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>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Yisheng Xie <ysxie@foxmail.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: Peter Rosin <peda@axentia.se>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: linux-fbdev@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-29-daniel.vetter@ffwll.ch