drm: Quieten [zero] EDID carping

We have a few displays in CI that always report their EDID as a bunch of
zeroes. This is consistent behaviour, so one assumes intentional
indication of an "absent" EDID. Flagging these consistent warnings
detracts from CI.

One option would be to ignore the zero EDIDs as intentional behaviour,
but Ville would like to keep the information available for debugging.
The simple alternative then is to reduce the loglevel for all the EDID
dumping from WARN to DEBUG so the information is present but not annoy
CI. Note that the bad EDID dumping is already only shown if
drm.debug=KMS, it's just the loglevel chosen was set to be caught by CI
if it ever occurred as it was expected to be an internal error not
external.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2203


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201029213042.11672-1-chris@chris-wilson.co.uk