[lvgl] Fix disp_bg_image when image not used;

Allow line points to be updated.
define gradients before use in styles

esphome/components/lvgl/__init__.py

@@ -322,8 +322,8 @@ async def to_code(configs):
             await encoders_to_code(lv_component, config, default_group)
             await keypads_to_code(lv_component, config, default_group)
             await theme_to_code(config)
-            await styles_to_code(config)
             await gradients_to_code(config)
+            await styles_to_code(config)
             await set_obj_properties(lv_scr_act, config)
             await add_widgets(lv_scr_act, config)
             await add_pages(lv_component, config)

esphome/components/lvgl/schemas.py

@@ -341,9 +341,15 @@ FLEX_OBJ_SCHEMA = {
     cv.Optional(df.CONF_FLEX_GROW): cv.int_,
 }
 
+
+def bg_image_validator(value):
+    add_lv_use("img", "label")
+    return lv_image(value)
+
+
 DISP_BG_SCHEMA = cv.Schema(
     {
-        cv.Optional(df.CONF_DISP_BG_IMAGE): lv_image,
+        cv.Optional(df.CONF_DISP_BG_IMAGE): bg_image_validator,
         cv.Optional(df.CONF_DISP_BG_COLOR): lv_color,
     }
 )

esphome/components/lvgl/widgets/line.py

@@ -39,7 +39,10 @@ LINE_SCHEMA = {
 class LineType(WidgetType):
     def __init__(self):
         super().__init__(
-            CONF_LINE, LvType("lv_line_t"), (CONF_MAIN,), LINE_SCHEMA, modify_schema={}
+            CONF_LINE,
+            LvType("lv_line_t"),
+            (CONF_MAIN,),
+            LINE_SCHEMA,
         )
 
     async def to_code(self, w: Widget, config):