stmhal: Enable frozenset. Takes 292 text bytes in ROM.

stmhal/mpconfigport.h

@@ -32,6 +32,7 @@
 #define MICROPY_ENABLE_FINALISER    (1)
 #define MICROPY_ENABLE_REPL_HELPERS (1)
 #define MICROPY_ENABLE_SOURCE_LINE  (1)
+#define MICROPY_ENABLE_FROZENSET    (1)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_FLOAT)
 #define MICROPY_PATH_MAX            (128)