esp32: Enable platform module with IDF version.

Output looks like this:

    >>> import platform
    >>> platform.libc_ver()
    ('newlib', '3.0.0')
    >>> platform.platform()
    'MicroPython-1.17.0-xtensa-IDFv4.2.2-with-newlib3.0.0'
    >>> platform.python_compiler()
    'GCC 8.4.0'
Signed-off-by: Damien George <damien@micropython.org>

ports/esp32/mpconfigport.h

@@ -195,6 +195,7 @@
 #define MICROPY_PY_FRAMEBUF                 (1)
 #define MICROPY_PY_BTREE                    (1)
 #define MICROPY_PY_ONEWIRE                  (1)
+#define MICROPY_PY_UPLATFORM                (1)
 #define MICROPY_PY_USOCKET_EVENTS           (MICROPY_PY_WEBREPL)
 #define MICROPY_PY_BLUETOOTH_RANDOM_ADDR    (1)
 #define MICROPY_PY_BLUETOOTH_DEFAULT_GAP_NAME ("ESP32")

ports/esp32/mphalport.h

@@ -35,6 +35,8 @@
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 
+#define MICROPY_PLATFORM_VERSION "IDF" IDF_VER
+
 // The core that the MicroPython task(s) are pinned to.
 // Until we move to IDF 4.2+, we need NimBLE on core 0, and for synchronisation
 // with the ringbuffer and scheduler MP needs to be on the same core.