stmhal/spi: Use software SPI if no periph id given, even if pins given.

It's simpler to just default to always using software SPI if no specific
peripheral id/name is given.  To use hardware SPI users must specify a
hardware peripheral id as the first parameter to the SPI constructor.

stmhal/spi.c

@@ -868,7 +868,7 @@ STATIC void machine_hard_spi_deinit(mp_obj_t self);
 
 STATIC mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
     static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_id,       MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_id,       MP_ARG_OBJ, {.u_obj = MP_OBJ_NEW_SMALL_INT(-1)} },
         { MP_QSTR_baudrate, MP_ARG_INT, {.u_int = 500000} },
         { MP_QSTR_polarity, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
         { MP_QSTR_phase,    MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
@@ -883,11 +883,7 @@ STATIC mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, s
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
-    if (args[ARG_NEW_id].u_obj == MP_OBJ_NULL) {
-        // no peripheral id given
-        // we use software SPI for now but should support hardware if pins allow it
-        return machine_soft_spi_make_new(args);
-    } else if (args[ARG_NEW_id].u_obj == MP_OBJ_NEW_SMALL_INT(-1)) {
+    if (args[ARG_NEW_id].u_obj == MP_OBJ_NEW_SMALL_INT(-1)) {
         // software SPI
         return machine_soft_spi_make_new(args);
     } else {