drm/amd/display: Do DIO FIFO enable after DP video stream enable

[Why]
Avoids a race condition where DIO FIFO can underflow due to no incoming
data available.

[How]
Shift the FIFO enable below stream enable.

Make sure fullness level is written before the DIO reset takes place
and that we're not doing it twice.

Reviewed-by: Syed Hassan <Syed.Hassan@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>