drm: Fix primary plane size for stereo doubled modes for legacy setcrtc

Properly double the hdisplay/vdisplay timings that we use as the primary
plane size with stereo doubled modes. Otherwise the modeset gets
rejected on machines where the primary plane must be fullscreen, and on
the rest only the first eye would get a visible plane.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org #v3.19+
Fixes: 042652ed ("drm/atomic-helper: implementatations for legacy interfaces")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447686157-29607-1-git-send-email-ville.syrjala@linux.intel.com


Testcase: igt/kms_3d
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>