extmod/moduselect: Conditionally compile select().

This adds #if MICROPY_PY_USELECT_SELECT around the uselect.select()
function. According to the docs, this function is only for CPython
compatibility and should not normally be used. So we can disable it
and save a few bytes of flash space where possible.

Signed-off-by: David Lechner <david@pybricks.com>

py/mpconfig.h

@@ -1316,6 +1316,13 @@ typedef double mp_float_t;
 #define MICROPY_PY_USELECT (0)
 #endif
 
+// Whether to enable the select() function in the "uselect" module (baremetal
+// implementation). This is present for compatibility but can be disabled to
+// save space.
+#ifndef MICROPY_PY_USELECT_SELECT
+#define MICROPY_PY_USELECT_SELECT (1)
+#endif
+
 // Whether to provide "utime" module functions implementation
 // in terms of mp_hal_* functions.
 #ifndef MICROPY_PY_UTIME_MP_HAL