esp32/machine_hw_spi: Release GIL during transfers.

Release the GIL while waiting for SPI transfers to complete to allow other
threads to make progress.

Fixes micropython#7662.

Author: jonathanhogg

ports/esp32/machine_hw_spi.c

@@ -346,15 +346,19 @@ STATIC void machine_hw_spi_transfer(mp_obj_base_t *self_in, size_t len, const ui
 
             if (offset > 0) {
                 // wait for previously queued transaction
+                MP_THREAD_GIL_EXIT();
                 spi_device_get_trans_result(self->spi, &result, portMAX_DELAY);
+                MP_THREAD_GIL_ENTER();
             }
 
             // doesn't need ceil(); loop ends when bits_remaining is 0
             offset += transaction->length / 8;
         }
 
         // wait for last transaction
+        MP_THREAD_GIL_EXIT();
         spi_device_get_trans_result(self->spi, &result, portMAX_DELAY);
+        MP_THREAD_GIL_ENTER();
         spi_device_release_bus(self->spi);
     }
 }