drm/radeon/kms: always do extended edid probe

Rather than having a quirk list just always check the EDID header
when probing.  This is the recommended behavior according to the
display team.  This avoids problems with improperly terminated
i2c lines on some boards.  This is also what the proprietary
driver does.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>