drm/amd/display: lttpr cap should be nrd cap in bw_alloc mode

drm/amd/display: lttpr cap should be nrd cap in bw_alloc mode

[WHY]
When bw allocation mode enabled, dpia may reports lttpr cap with
reduced common cap. It would cause driver not start pre-training with
max available bandwidth.

[How]
When bw allocation mode enabled, use NRD cap as lttpr cap.

Reviewed-by: Cruise Hung <cruise.hung@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Peichen Huang <PeiChen.Huang@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>