drm/edid: add drm_edid helper for drm_detect_monitor_audio()

We'll need to propagate drm_edid everywhere.

v2: Handle NULL EDID pointer (Ville, CI)

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ea33244c473ace1bc72a7e87f97580f00705a683.1652097712.git.jani.nikula@intel.com