py/mpconfig: Enable io.IOBase at core feature level.

IOBase is quite an important building block of other parts of the system,
such as `mpremote mount` and running .mpy and native tests.

This feature costs +244 bytes of firmware size on ARM Thumb2 architectures,
which is worth the cost for the extra features it enables.

The change here means that `io.IOBase` is now enabled on all nrf boards,
(previously it was only nRF52840 and nRF9160) and also B_L072Z_LRWAN1
(there is no change to other ports or boards).

Signed-off-by: Damien George <[email protected]>

Author: dpgeorge

py/mpconfig.h

@@ -1469,7 +1469,7 @@ typedef double mp_float_t;
 
 // Whether to provide "io.IOBase" class to support user streams
 #ifndef MICROPY_PY_IO_IOBASE
-#define MICROPY_PY_IO_IOBASE (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_EXTRA_FEATURES)
+#define MICROPY_PY_IO_IOBASE (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES)
 #endif
 
 // Whether to provide "io.BytesIO" class