RPi Pico port (#42)

based on work of @jgpeiro
https://forum.lvgl.io/t/build-lvgl-for-raspberry-pi-pico/5543 .

* add brief documentation on building the port

Related PR: lvgl/lv_binding_micropython#174

Author: eudoxos

README.md

@@ -58,6 +58,15 @@ For more details please refer to [Micropython ESP32 README](https://github.com/m
 
 Refer to the README of the `lvgl_javascript` branch: https://github.com/lvgl/lv_micropython/tree/lvgl_javascript#for-javascript-port
 
+### For Raspberry Pi Pico port
+
+This port uses [Micropython infrastructure for C modules](https://docs.micropython.org/en/latest/develop/cmodules.html#compiling-the-cmodule-into-micropython) and `USER_C_MODULES` must be given:
+
+```
+cd ports/rp2
+make USER_C_MODULES=../../lv_bindings/bindings.cmake
+```
+
 ## Super Simple Example
 
 First, LVGL needs to be imported and initialized

ports/rp2/mpconfigport.h

@@ -33,6 +33,9 @@
 
 #include "mpconfigboard.h"
 
+#define MICROPY_PY_LVGL                         (1)
+#define MICROPY_PY_LODEPNG                      (1)
+
 // Board and hardware specific configuration
 #define MICROPY_HW_MCU_NAME                     "RP2040"
 #define MICROPY_HW_ENABLE_UART_REPL             (0) // useful if there is no USB
@@ -162,15 +165,47 @@ extern const struct _mp_obj_module_t mp_module_onewire;
 extern const struct _mp_obj_module_t mp_module_rp2;
 extern const struct _mp_obj_module_t mp_module_uos;
 extern const struct _mp_obj_module_t mp_module_utime;
+extern const struct _mp_obj_module_t mp_module_lvgl;
+extern const struct _mp_obj_module_t mp_module_lodepng;
+
+#if MICROPY_PY_LVGL
+#define MICROPY_PORT_LVGL_DEF \
+    { MP_OBJ_NEW_QSTR(MP_QSTR_lvgl), (mp_obj_t)&mp_module_lvgl },
+
+#else
+#define MICROPY_PORT_LVGL_DEF
+#endif
+
+#if MICROPY_PY_LODEPNG
+#define MICROPY_PORT_LODEPNG_DEF { MP_OBJ_NEW_QSTR(MP_QSTR_lodepng), (mp_obj_t)&mp_module_lodepng },
+#else
+#define MICROPY_PORT_LODEPNG_DEF
+#endif
 
 #define MICROPY_PORT_BUILTIN_MODULES \
     { MP_OBJ_NEW_QSTR(MP_QSTR_machine), (mp_obj_t)&mp_module_machine }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR__onewire), (mp_obj_t)&mp_module_onewire }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR__rp2), (mp_obj_t)&mp_module_rp2 }, \
     { MP_ROM_QSTR(MP_QSTR_uos), MP_ROM_PTR(&mp_module_uos) }, \
     { MP_ROM_QSTR(MP_QSTR_utime), MP_ROM_PTR(&mp_module_utime) }, \
+    MICROPY_PORT_LVGL_DEF \
+    MICROPY_PORT_LODEPNG_DEF \
+
+#if MICROPY_PY_LVGL
+#ifndef MICROPY_INCLUDED_PY_MPSTATE_H
+#define MICROPY_INCLUDED_PY_MPSTATE_H
+#include "lib/lv_bindings/lvgl/src/misc/lv_gc.h"
+#undef MICROPY_INCLUDED_PY_MPSTATE_H
+#else
+#include "lib/lv_bindings/lvgl/src/misc/lv_gc.h"
+#endif
+#else
+#define LV_ROOTS
+#endif
 
 #define MICROPY_PORT_ROOT_POINTERS \
+    LV_ROOTS \
+    void *mp_lv_user_data; \
     const char *readline_hist[8]; \
     void *machine_pin_irq_obj[30]; \
     void *rp2_pio_irq_obj[2]; \