drm/i915: Add HDCP capability info to i915_display_info.

To identify the HDCP capability of the display connected to CI
systems, we need to add the hdcp capability probing in i915_display_info.

This will also help to populate the HDCP capability of the CI systems
to CI H/W logs maintained at https://intel-gfx-ci.01.org/hardware/

.
It will facilitate to determine the kms_content_protection behavior on
a particular CI system.

v2: Reused the intel_hdcp_info() in i915_hdcp_sink_capability_show(). [Ram]
    Shifted intel_hdcp_info() to the end of intel_dp_info. [Ram]
v3: used seq_puts() instead of seq_pritnf(). [Ram]

Cc: daniel.vetter@intel.com
Cc: ramalingam.c@intel.com
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190719055513.2089-1-anshuman.gupta@intel.com