drm/i915: Delete fb, x and y parameters from mode set functions

We don't need to pass it down the call chain anymore now that the plane
state is set up properly.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>