ports: Enable os.sync() for esp32, esp8266, rp2, mimxrt, samd51.

These have by default FAT support.  The SAMD21 build does not support FAT.
The nrf port also implements os.sync(), but has it's own copy of moduos.c.

Code size increases seen: 40 to 56 bytes.

Signed-off-by: robert-hh <robert@hammelrath.com>

ports/esp32/mpconfigport.h

@@ -91,6 +91,7 @@
 #define MICROPY_PY_UOS_INCLUDEFILE          "ports/esp32/moduos.c"
 #define MICROPY_PY_OS_DUPTERM               (1)
 #define MICROPY_PY_UOS_DUPTERM_NOTIFY       (1)
+#define MICROPY_PY_UOS_SYNC                 (1)
 #define MICROPY_PY_UOS_UNAME                (1)
 #define MICROPY_PY_UOS_URANDOM              (1)
 #define MICROPY_PY_MACHINE                  (1)