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.c b/drivers/gpu/drm/exynos/exynos_drm_plane.c
index e668fcd..e45730a 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_plane.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_plane.c
@@ -280,7 +280,7 @@
 
 int exynos_plane_init(struct drm_device *dev,
 		      struct exynos_drm_plane *exynos_plane,
-		      unsigned long possible_crtcs,
+		      unsigned int index, unsigned long possible_crtcs,
 		      const struct exynos_drm_plane_config *config)
 {
 	int err;
@@ -298,7 +298,7 @@
 
 	drm_plane_helper_add(&exynos_plane->base, &plane_helper_funcs);
 
-	exynos_plane->zpos = config->zpos;
+	exynos_plane->index = index;
 	exynos_plane->config = config;
 
 	if (config->type == DRM_PLANE_TYPE_OVERLAY)