drm/vc4: Take margin setup into account when updating planes

Applyin margins is just a matter of scaling all planes appropriately
and adjusting the CRTC X/Y offset to account for the
left/right/top/bottom borders.

Create a vc4_plane_margins_adj() function doing that and call it from
vc4_plane_setup_clipping_and_scaling() so that we are ready to attach
margins properties to the HDMI connector.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181206142439.10441-5-boris.brezillon@bootlin.com

drivers/gpu/drm/vc4/vc4_drv.h

@@ -707,6 +707,9 @@ bool vc4_crtc_get_scanoutpos(struct drm_device *dev, unsigned int crtc_id,
 			     const struct drm_display_mode *mode);
 void vc4_crtc_handle_vblank(struct vc4_crtc *crtc);
 void vc4_crtc_txp_armed(struct drm_crtc_state *state);
+void vc4_crtc_get_margins(struct drm_crtc_state *state,
+			  unsigned int *right, unsigned int *left,
+			  unsigned int *top, unsigned int *bottom);
 
 /* vc4_debugfs.c */
 int vc4_debugfs_init(struct drm_minor *minor);