drm/i915/hdcp: Nuke Platform check for mst hdcp init

Earlier HDCP over MST support was added for TGL Platform.
Extending it to all future platfroms.

v2:
- Remove the platform check and commit log changes. [Jani]

Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210705122208.25618-1-anshuman.gupta@intel.com