drm/i915: Use str_enabled_disabled()

Remove the local enableddisabled() implementation and adopt the
str_enabled_disabled() from linux/string_helpers.h.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220225234631.3725943-3-lucas.demarchi@intel.com