drm/exynos: rename zpos to index

This patch renames zpos entry to index, because in most places it is
used as index for selecting hardware layer/window instead of
configurable layer position. This will later enable to make the zpos
property configurable.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
diff --git a/drivers/gpu/drm/exynos/exynos_drm_plane.h b/drivers/gpu/drm/exynos/exynos_drm_plane.h
index 0dd0965..9aafad1 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_plane.h
+++ b/drivers/gpu/drm/exynos/exynos_drm_plane.h
@@ -10,6 +10,6 @@
  */
 
 int exynos_plane_init(struct drm_device *dev,
-		      struct exynos_drm_plane *exynos_plane,
+		      struct exynos_drm_plane *exynos_plane, unsigned int index,
 		      unsigned long possible_crtcs,
 		      const struct exynos_drm_plane_config *config);