Add edid_block_check() that only checks the EDID block validity, without
any actions. Turns out it's simple and crystal clear.

Rewrite drm_edid_block_valid() around it, keeping all the functionality
fairly closely the same, warts and all. Turns out it's incredibly
complicated for a function you'd expect to be simple, with all the
fixing and printing and special casing. (Maybe we'll want to simplify it
in the future.)

To slightly simplify, drop the warning for EDID minor revisions > 4.

v2:
- Fix edid_fixup clamp (Ville)
- s/base/is_base_block/ (Ville)

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/b7d108b69acccb7dccbdecc0ca06c2b3ca2e33ca.1648752228.git.jani.nikula@intel.com