drm/atomic: Unify conflicting encoder handling.

Currently we use a flag to change behavior in atomic commit
whether a conflicting encoder should be enabled or disabled.
This is used for the legacy set_config helper, which disables
connectors that have a conflicting encoder but not part of the
active crtc list.

There's no need for this to be handled in atomic commit, it
could be done in the set_config helper instead. This will
let the atomic check function reject any conflicting encoders,
while set_config can disable conflicting crtc's. This makes it
possible to recalculate the changed flags in 1 loop.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1491477543-31257-2-git-send-email-maarten.lankhorst@linux.intel.com