convert lvgl from submodule to a plain old directory

lib/lvgl/.gitignore

@@ -0,0 +1,27 @@
+**/*.o
+**/*bin
+**/*.swp
+**/*.swo
+**/*.gcda
+**/*.gcno
+tags
+docs/api_doc
+scripts/cppcheck_res.txt
+scripts/built_in_font/lv_font_*
+docs/doxygen_html
+docs/xml
+docs/examples.md
+docs/out_latex
+docs/_static/built_lv_examples
+docs/LVGL.pdf
+docs/env
+out_html
+__pycache__
+/emscripten_builder
+test_screenshot_error.h
+build/
+tests/build_*/
+tests/report/
+.DS_Store
+.vscode
+*.bak