This PR adds an LVGL App that executes NSH Commands (entered with a Touchscreen Keyboard) and renders the NSH Output. The app follows the same design as the `lvgldemo` app and is explained here: ["NuttX RTOS for PinePhone: LVGL Terminal for NSH Shell"](https://lupyuen.github.io/articles/terminal)
`examples/README.md`: Added doc for `lvglterm` app
`examples/lvglterm/lvglterm.c`: LVGL Terminal App
`examples/lvglterm/Makefile`, `Make.defs`: Makefile for LVGL Terminal
`examples/lvglterm/Kconfig`: Added menuconfig option for "Application Configuration > Examples > LVGL Terminal"
