drm/i915/hdcp: Move to direct reads for HDCP

Even for MST scenarios we need to do direct reads only on the
immediate downstream device the rest of the authentication is taken
care by that device. Remote reads will only be used to check
capability of the monitors in MST topology.

--v2
-Add fixes tag [Ankit]
-Derive aux where needed rather than through a function [Ankit]

Fixes: ae4f902b ("drm/i915/hdcp: Send the correct aux for DPMST HDCP scenario")
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240223081453.1576918-3-suraj.kandpal@intel.com