drm/amd/display: adopt DP2.0 LT SCR revision 8

[how]
revision 8 SCR requires DP Source to write TPS2 and FFE lane adjustment
in one 5 byte write aux transaction.
It specifies to read aux rd interval value as soon as we turn on TPS1
pattern.

Cc: Wayne Lin <wayne.lin@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>