drm/edid: split drm_edid block count helper

Split the drm_edid block count helper to a base version that reports the
block count indicated by EDID contents, and another on top that limits
the block count based on size allocated for the EDID.

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/a7d63878c7fb3dd6f3b987f5257897113797b94f.1666614699.git.jani.nikula@intel.com