drm/amd/display: Avoid HDCP initialization in devices without output

The HDCP feature requires at least one connector attached to the device;
however, some GPUs do not have a physical output, making the HDCP
initialization irrelevant. This patch disables HDCP initialization when
the graphic card does not have output.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org