async_spi: SPI transfers for asyncio

ports/raspberrypi/common-hal/async_spi/SPI.h

@@ -0,0 +1,34 @@
+// This file is part of the CircuitPython project: https://circuitpython.org
+//
+// SPDX-FileCopyrightText: Copyright (c) 2026 Vladimir Smitka
+//
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include "py/obj.h"
+#include "common-hal/microcontroller/Pin.h"
+#include "supervisor/shared/async_flag.h"
+#include "supervisor/shared/awaitable.h"
+
+#include "hardware/spi.h"
+
+typedef struct {
+    mp_obj_base_t base;
+    circuitpy_async_lock_obj_t lock;
+    spi_inst_t *peripheral;
+    const mcu_pin_obj_t *clock;         // NULL once deinited
+    const mcu_pin_obj_t *mosi;
+    const mcu_pin_obj_t *miso;
+    uint32_t target_frequency;
+    int32_t real_frequency;
+    uint8_t polarity;
+    uint8_t phase;
+    uint8_t bits;
+    bool async_active;                  // an async DMA transfer may still be running
+    bool dma_kept;                      // dma_tx and dma_rx are ours until deinit
+    uint8_t dma_tx;
+    uint8_t dma_rx;
+    uint8_t one_byte;                   // the one-byte side of an async write (RX) or read (TX)
+    circuitpy_async_flag_t *async_done;
+} async_spi_spi_obj_t;

ports/raspberrypi/common-hal/async_spi/__init__.c

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+// This file is part of the CircuitPython project: https://circuitpython.org
+//
+// SPDX-FileCopyrightText: Copyright (c) 2026 Vladimir Smitka
+//
+// SPDX-License-Identifier: MIT
+
+// No async_spi module functions.