feat: SPI DMA

Squashed commit of the following:

commit c3e1f696b4fbafb6dd30c6934e4c7c181562e055
Author: kuwoyuki <kuwoyuki@cock.li>
Date:   Sat Oct 12 20:43:12 2024 +0600

    chore: spi dma

commit d1e7df60be3e06ed85ce8639516e299085d3c72b
Author: kuwoyuki <kuwoyuki@cock.li>
Date:   Sat Oct 12 15:14:11 2024 +0600

    static dummies

commit 81682428b471f825e3350e37aa74c373b46d4fef
Author: kuwoyuki <kuwoyuki@cock.li>
Date:   Sat Oct 12 14:45:39 2024 +0600

    dma works?

commit 150c97a4b566712a502d8a2861a2dc0864324d61
Author: kuwoyuki <kuwoyuki@cock.li>
Date:   Sat Oct 12 02:07:39 2024 +0600

    dma?

include/spi_dma.h

@@ -0,0 +1,35 @@
+#ifndef SPI_DMA_H
+#define SPI_DMA_H
+
+#include "ch32v003fun.h"
+
+typedef enum {
+  IDLE,
+  TRANSMITTING,
+  RECEIVING,
+  TX_DONE,
+  RX_DONE
+} transfer_state_t;
+
+// SPI DMA initialization function
+void init_spidma(void);
+
+// SPI DMA buffer read
+void spidma_read_buffer(uint8_t *buf, uint16_t len);
+
+// SPI DMA buffer write
+void spidma_write_buffer(uint8_t *buf, uint16_t len);
+
+// SPI (non-DMA) byte read
+uint8_t spi_read_byte();
+
+// SPI (non-DMA) byte write
+void spi_write_byte(uint8_t byte);
+
+// activate CS
+void spi_select(void);
+
+// deactivate CS
+void spi_unselect(void);
+
+#endif  // SPI_DMA_H