drm/edid: add block count and data helper functions for drm_edid

Add drm_edid based block count and data access helper functions that
take the EDID allocated size into account.

At the moment, the allocated size should always match the EDID size
indicated by the extension count, but this will change in the future.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1a68c8667a88e7c451b001ad8bd86c8badb57fb8.1654674560.git.jani.nikula@intel.com