samd/machine_spi: Implement spi.deinit() and simplify sercom_deinit_all.

The sercom_deinit_all() function does not need the object pointers.

ports/samd/machine_spi.c

@@ -254,17 +254,23 @@ STATIC mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, s
     return self;
 }
 
+STATIC void machine_sercom_deinit(mp_obj_base_t *self_in) {
+    machine_spi_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    Sercom *spi = sercom_instance[self->id];
+    // Disable interrupts (if any)
+    spi->SPI.INTENCLR.reg = 0xff;
+    sercom_enable(spi, 0);
+    // clear table entry of spi
+    sercom_table[self->id] = NULL;
+}
+
 void sercom_deinit_all(void) {
     for (int i = 0; i < SERCOM_INST_NUM; i++) {
-        if (sercom_table[i] != NULL) {
-            machine_spi_obj_t *self = sercom_table[i];
-            Sercom *spi = sercom_instance[self->id];
-            // Disable interrupts (if any)
-            spi->SPI.INTENCLR.reg = 0xff;
-            // clear table entry of spi
-            sercom_table[i] = NULL;
-            sercom_enable(spi, 0);
-        }
+        Sercom *spi = sercom_instance[i];
+        spi->SPI.INTENCLR.reg = 0xff;
+        sercom_register_irq(i, NULL);
+        sercom_enable(spi, 0);
+        sercom_table[i] = NULL;
     }
 }
 
@@ -316,6 +322,7 @@ STATIC void machine_spi_transfer(mp_obj_base_t *self_in, size_t len, const uint8
 
 STATIC const mp_machine_spi_p_t machine_spi_p = {
     .init = machine_spi_init,
+    .deinit = machine_sercom_deinit,
     .transfer = machine_spi_transfer,
 };