drm/amd/display: Setup stream encoder before link enable for TMDS

[Why]
HDMI spec requires TMDS clock to be not more than 340MHz. Stream encoder ensure
this requirement but driver enable stream encoder later than PHY. So PHY will
output full speed TMDS clock first.

[How]
Enable stream encoder first in TMDS case.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alan Liu <haoping.liu@amd.com>
Signed-off-by: JinZe Xu <jinze.xu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>