[Why]
We should check MST BU support capability on output port before building
vsc info packet.

[How]
Add a new definition for port and sink capability check.

Signed-off-by: Martin Tsai <martin.tsai@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>