drm: Add helper to compare edids.

Many drivers would benefit from using
drm helper to compare edid, rather
than bothering with own implementation.

v2: Added documentation for this function.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200630002700.5451-2-kunal1.joshi@intel.com