drm/amd/display: Old sequence for HUBP blank

New proposed sequence for HUBP blanking causes regressions where the
hardware would fail to enter blank which triggers an assert in the new
sequence. This change brings back the old sequence.

Fixes: 985faf2c ("drm/amd/display: New sequence for HUBP blank")
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>