drm/amd/display: Move mod_hdcp_displays to mod_hdcp struct

[Why]
Reset connection is called before remove display in mod_hdcp. When
remove display is called, the display structure has been zeroed from
reset connection. Since no displays can be found, remove display does
not properly reset the hardware. This causes validation errors when
another display is plugged into a different port afterwards.

[How]
Moved displays structure out of connections structure. Displays
structure is now directly within mod_hdcp. Displays is no longer zeroed
when reset connection is called.

Signed-off-by: Isabel Zhang <isabel.zhang@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>