rp2: Enable uerrno module.
Fixes
#define MICROPY_PY_SYS_STDFILES (1)
#define MICROPY_PY_SYS_STDIO_BUFFER (1)
#define MICROPY_PY_SYS_PLATFORM "rp2"
+#define MICROPY_PY_UERRNO (1)
#define MICROPY_PY_THREAD (1)
#define MICROPY_PY_THREAD_GIL (0)
