drm/displayid: rename displayid_hdr to displayid_header

Avoid any confusion with High Dynamic Range. No functional changes.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ce083bd2789c7e22a91710726162287db88e3f6c.1617024940.git.jani.nikula@intel.com