#401 Register automatic git submodules handling

Summary

Adds automatic submodule initialization for lvgl and pycparser to both Make and CMake build systems. This removes the manual step of running git submodule update --init before building. Both implementations hook into MicroPython's existing submodules target - Make appends to the target directly, while CMake registers via the ECHO_SUBMODULES mechanism. Also adds validation in CMake to catch missing submodules at configuration time with a helpful error message.

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Summary by cubic

Automatically initializes lvgl and pycparser git submodules in both Make and CMake builds to remove the manual step. CMake also fails fast with a clear error if lvgl isn’t initialized.

• New Features
  • Make: extends MicroPython’s submodules target to sync/init lvgl and pycparser.
  • CMake: registers both via ECHO_SUBMODULES; if lvgl/README.md is missing, configuration fails and suggests make BOARD=${MICROPY_BOARD} submodules.