Revert "drm/amd/display: disable dcn20 abm feature for bring up"

commit 14ed1c908a7a623cc0cbf0203f8201d1b7d31d16 upstream.

This reverts commit 96cb7cf1.

This change was used for DCN2 bringup and is no longer desired.
In fact it breaks backlight on DCN2 systems.

Cc: Alexander Monakov <amonakov@ispras.ru>
Cc: Hersen Wu <hersenxs.wu@amd.com>
Cc: Anthony Koo <Anthony.Koo@amd.com>
Cc: Michael Chiu <Michael.Chiu@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reported-and-tested-by: Alexander Monakov <amonakov@ispras.ru>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>