Revert "uxa: Do not change DPMS mode on unconnected outputs"

Revert "uxa: Do not change DPMS mode on unconnected outputs"

This reverts commit 4497212307dee5e35bc6836201738a2fdb559020.

Unfortunately, this simple fix does not work for UXA as DPMS is used by
the xserver to turn off CRTCs and outputs. Since UXA does not implement
CRTC DPMS, this commit causes us to fail to turn off outputs.

The kernel has been fixed up in the meantime and that commit has been
recommended to be backported to all stable kernels:

commit c9976dcf55c8aaa7037427b239f15e5acfc01a3a
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sun Sep 29 19:15:07 2013 +0100

    drm/i915: Only apply DPMS to the encoder if enabled

so it should be safe for UXA to rely on its old behaviour.

Bugzilla: https://code.google.com/p/chromium/issues/detail?id=341135
References: https://bugs.freedesktop.org/show_bug.cgi?id=68030
Suggested-by: Dominik Behr <dbehr@google.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>