drm/amd/display: Restore backlight brightness after system resume

commit bb264220d9316f6bd7c1fd84b8da398c93912931 upstream.

Laptops with AMD APU doesn't restore display backlight brightness after
system resume.

This issue started when DC was introduced.

Let's use BL_CORE_SUSPENDRESUME so the backlight core calls
update_status callback after system resume to restore the backlight
level.

Tested on Dell Inspiron 3180 (Stoney Ridge) and Dell Latitude 5495
(Raven Ridge).

Cc: <stable@vger.kernel.org>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>