drm/amd/display: validate extended dongle caps

drm/amd/display: validate extended dongle caps

[why]
Some dongle doesn't have a valid extended dongle caps,
but we still set the extended dongle caps to be valid.
This causes validation fails for all timing.

[how]
If no dp_hdmi_max_pixel_clk is provided,
don't use extended dongle caps.

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Abdoulaye Berthe <Abdoulaye.Berthe@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>