drm: Add reference counting on HDR metadata blob

This adds reference count for HDR metadata blob,
handled as part of duplicate and destroy connector
state functions.

v2: Removed the hdr_metadata_changed initialization as
the variable is dropped and not required.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1558015817-12025-3-git-send-email-uma.shankar@intel.com