drm/i915: Only enable the plane after setting the fb base (pre-ILK)

When enabling the plane, it is helpful to have already pointed that
plane to valid memory or else we may incur the wrath of a PGTBL_ER.
This code preserved the behaviour from the bad old days for unknown
reasons...

Found by assert_fb_bound_for_plane().

References: https://bugs.freedesktop.org/show_bug.cgi?id=36246
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_display.c

@@ -5154,8 +5154,6 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 
 	I915_WRITE(DSPCNTR(plane), dspcntr);
 	POSTING_READ(DSPCNTR(plane));
-	if (!HAS_PCH_SPLIT(dev))
-		intel_enable_plane(dev_priv, plane, pipe);
 
 	ret = intel_pipe_set_base(crtc, x, y, old_fb);