stmhal: Enable help('modules') feature.

stmhal/help.c

@@ -67,4 +67,5 @@ const char *stmhal_help_text =
 "  CTRL-E        -- on a blank line, enter paste mode\n"
 "\n"
 "For further help on a specific object, type help(obj)\n"
+"For a list of available modules, type help('modules')\n"
 ;

stmhal/mpconfigport.h

@@ -78,6 +78,7 @@
 #define MICROPY_PY_BUILTINS_COMPILE (1)
 #define MICROPY_PY_BUILTINS_HELP    (1)
 #define MICROPY_PY_BUILTINS_HELP_TEXT stmhal_help_text
+#define MICROPY_PY_BUILTINS_HELP_MODULES (1)
 #define MICROPY_PY_ALL_SPECIAL_METHODS (1)
 #define MICROPY_PY_MICROPYTHON_MEM_INFO (1)
 #define MICROPY_PY_ARRAY_SLICE_ASSIGN (1)