drm/amd/display: Prevent IPX From Link Detect and Set Mode

IPX involvment proven to affect LT, causing link loss. Need to prevent
IPX enabled in LT process in which link detect and set mode are main
procedures that have LT taken place.

Reviewed-by: Roman Li <roman.li@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>