drm/amd/display: Update FIXED_VS retimer training pattern delay

[WHY]
Needed for PHY patterns as well to perform electrical compliance.
Also need to increase wait time from 30ms to 50ms to resolve very
intermittent UHBR20 link training failures.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>