drm/i915: Another fbdev hack to avoid PSR on fbcon.

drm/i915: Another fbdev hack to avoid PSR on fbcon.

With unified modeset and flip paths introduced recently when switching
to fbcon PSR was being disabled on fb_set_par path but re-enabled on
fb_pan_display one, causing missed screen updates and un unusable
console.

Regression introduced with:

commit 4b7967fe459a73a19af23c82279c43f522b6ac37
Author: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Date:   Tue Apr 21 17:13:13 2015 +0300

    drm/i915: Unify modeset and flip paths of intel_crtc_set_config()

Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>