drm/amd/display: Disable FRL and add module param to enable it

drm/amd/display: Disable FRL and add module param to enable it

FRL links don't yet support VRR. If we enable it by default
users will see a functional regression when connected to an FRL
capable display as the driver will now default to FRL and not
allow VRR.

VRR support will come soon, so instead of making an elaborate
TMDS fallback mechanism simply default FRL to disabled, but
provide a dcfeaturemask of 0x400 to enable it if anyone wants
to already try it out.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>