drm/amd/display: Add hdcp to Kconfig

[Why]
HDCP is not fully finished, so we need to be able to
build and run the driver without it.

[How]
Add a Kconfig to toggle it

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>