LVGL as a git submodule

Dind't update version, kept v8.3.11 for now, will look at it later. LV drivers are kept as is, as there is some custom patch on top.

In future should migrate to LVGL v9, where drivers ar integrated in the same tree.

Author: kristapsk

.gitmodules

@@ -2,3 +2,6 @@
 	path = lib/ini
 	url = https://github.com/ziglibs/ini.git
 	shallow = true
+[submodule "lib/lvgl"]
+	path = lib/lvgl
+	url = https://github.com/lvgl/lvgl.git