drm/print: group logging functions by prink or device based

In preparation for adding struct drm_device based logging, group the
existing functions by prink or struct device based logging. No
functional changes.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Sean Paul <sean@poorly.run>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/51c70d80e7dd06c49ba3be56fbb6ae70edddc102.1572258936.git.jani.nikula@intel.com