drm/i915/hdcp: Encapsulate hdcp_port_data to dig_port

hdcp_port_data is specific to a port on which HDCP
encryption is getting enabled, so encapsulate it to
intel_digital_port.
This will be required to enable HDCP 2.2 stream encryption.

v2:
- 's/port_data/hdcp_port_data'. [Ram]

Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Tested-by: Karthik B S <karthik.b.s@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210111081120.28417-12-anshuman.gupta@intel.com