drm/amd/display: Implement multiple secure display

[Why]
Current secure display only work with single display, now make it
work with multiple displays.

[How]
Create secure_display_context for each crtc instance to store its
own Region of Interest (ROI) information.

v2: squash in warning fix (Alex)

Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>