drm/amd/display: Don't set dpms_off for seamless boot

[Why]
eDPs fail to light up with seamless boot enabled

[How]
When seamless boot is enabled don't configure dpms_off
in disable_vbios_mode_if_required.

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Daniel Miess <daniel.miess@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>