drm/edid: add drm_edid helper for drm_edid_to_speaker_allocation()

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/770d095c93274969c4b86480e07044e16a7b5760.1652097712.git.jani.nikula@intel.com