drm/amd/display: Not fallback if link BW is smaller than req BW

[Why]
When the link BW is smaller than the request BW,
the DP LT just kept running and fallback to lower link config.
DP LT just aborted if is_hpd_pending bit is high.
But is_hpd_pending bit indicates a new HPD event received.
It doesn't mean the HPD is low.

[How]
Abort the DP LT if the link BW is smaller than the request BW.
Remove checking is_hpd_pending bit in DP LT.

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