drm/i915: fixup load-detect on enabled, but not active pipe

Somehow we have a fast-path that tries to avoid going through
the load-detect code when the encode already has a crtc associated.
But this fails horribly when the crtc is off. The load detect pipe
itself manages this case well (and also does not forget to restore the
dpms state), so just rip out this special case.

The issue seems to go back all the way to the commit that originally
introduced load-detection on the vga output:

commit e4a5d54f
Author: Ma Ling <ling.ma@intel.com>
Date:   Tue May 26 11:31:00 2009 +0800

    drm/i915: Add support for VGA load detection (pre-945).

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=43020


Reported-by: Jean Delvare <khali@linux-fr.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>