drm/edid: add iterator for EDID base and extension blocks

Add an iterator abstraction for going through all the EDID blocks.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ce02778b353b906c928268de9d7569d493a9be5d.1651569697.git.jani.nikula@intel.com