drm/i915: Attach HDR metadata property to connector

Attach HDR metadata property to connector object.

v2: Rebase

v3: Updated the property name as per updated name
while creating hdr metadata property

v4: Added platform check as suggested by Ville.

Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1558109949-3309-1-git-send-email-uma.shankar@intel.com