drm/nouveau/disp/mcp7x: disable dptmds workaround

commit 7dfee6827780d4228148263545af936d0cae8930 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>