doc: releases: 2.4: add LVGL v7 update details

Add details of the LVGL7 update (e.g. warn about higher ROM usage,
changed Kconfig defaults, ...)

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

doc/releases/release-notes-2.4.rst

@@ -267,6 +267,34 @@ Libraries / Subsystems
 * Power management:
 
 
+* LVGL
+
+  * Library has been updated to the new major release v7.0.2.
+
+  * It is important to note that v7 introduces multiple API changes and new
+    configuration settings, so applications developed on v6 or previous versions
+    will likely require some porting work. Refer to `LVGL 7 Release notes
+    <https://github.com/lvgl/lvgl/releases/tag/v7.0.0>`_ for more information.
+
+  * LVGL Kconfig constants have been aligned with upstream suggested defaults.
+    If your application relies on any of the following Kconfig defaults consider
+    checking if the new values are good or they need to be adjusted:
+
+    * :option:`CONFIG_LVGL_HOR_RES`
+    * :option:`CONFIG_LVGL_VER_RES`
+    * :option:`CONFIG_LVGL_DPI`
+    * :option:`CONFIG_LVGL_SCREEN_REFRESH_PERIOD`
+    * :option:`CONFIG_LVGL_INPUT_REFRESH_PERIOD`
+    * :option:`CONFIG_LVGL_INPUT_DRAG_THROW_SLOW_DOWN`
+    * :option:`CONFIG_LVGL_TEXT_LINE_BREAK_LONG_LEN`
+    * :option:`CONFIG_LVGL_OBJ_CHART_AXIS_TICK_LABEL_MAX_LEN`
+
+  * Note that ROM usage is significantly higher on v7 for minimal
+    configurations. This is in part due to new features such as the new drawing
+    system. LVGL maintainers are currently investigating ways for reducing the
+    library footprint when some options are not enabled, so you should wait for
+    future releases if higher ROM usage is a concern for your application.
+
 HALs
 ****