drm/nouveau/disp/mcp7x: disable dptmds workaround

commit 7dfee682 upstream.

The workaround appears to cause regressions on these boards, and from
inspection of RM traces, NVIDIA don't appear to do it on them either.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Tested-by: Roy Spliet <nouveau@spliet.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>