stm32/spibdev: Add option to configure SPI block dev to use QSPI flash.

To use QSPI (in software QSPI mode) the configuration needed is:

    #define MICROPY_HW_SPIFLASH_SIZE_BITS (n * 1024 * 1024)
    #define MICROPY_HW_SPIFLASH_CS      (pin_x1)
    #define MICROPY_HW_SPIFLASH_SCK     (pin_x2)
    #define MICROPY_HW_SPIFLASH_IO0     (pin_x3)
    #define MICROPY_HW_SPIFLASH_IO1     (pin_x4)
    #define MICROPY_HW_SPIFLASH_IO2     (pin_x5)
    #define MICROPY_HW_SPIFLASH_IO3     (pin_x6)

ports/stm32/Makefile

@@ -185,6 +185,7 @@ EXTMOD_SRC_C = $(addprefix extmod/,\
         )
 
 DRIVERS_SRC_C = $(addprefix drivers/,\
+	bus/softqspi.c \
 	memory/spiflash.c \
 	dht/dht.c \
 	)

ports/stm32/spibdev.c

@@ -36,6 +36,10 @@
 
 static uint32_t flash_tick_counter_last_write;
 
+#if defined(MICROPY_HW_SPIFLASH_MOSI)
+
+// External SPI flash uses standard SPI interface
+
 STATIC const mp_machine_soft_spi_obj_t spiflash_spi_bus = {
     .base = {&mp_machine_soft_spi_type},
     .delay_half = MICROPY_PY_MACHINE_SPI_MIN_DELAY,
@@ -53,6 +57,29 @@ STATIC const mp_spiflash_config_t spiflash_config = {
     .bus.u_spi.proto = &mp_machine_soft_spi_p,
 };
 
+#elif defined(MICROPY_HW_SPIFLASH_IO0)
+
+// External SPI flash uses quad SPI interface
+
+#include "drivers/bus/qspi.h"
+
+STATIC const mp_soft_qspi_obj_t soft_qspi_bus = {
+    .cs = &MICROPY_HW_SPIFLASH_CS,
+    .clk = &MICROPY_HW_SPIFLASH_SCK,
+    .io0 = &MICROPY_HW_SPIFLASH_IO0,
+    .io1 = &MICROPY_HW_SPIFLASH_IO1,
+    .io2 = &MICROPY_HW_SPIFLASH_IO2,
+    .io3 = &MICROPY_HW_SPIFLASH_IO3,
+};
+
+STATIC const mp_spiflash_config_t spiflash_config = {
+    .bus_kind = MP_SPIFLASH_BUS_QSPI,
+    .bus.u_qspi.data = (void*)&soft_qspi_bus,
+    .bus.u_qspi.proto = &mp_soft_qspi_proto,
+};
+
+#endif
+
 STATIC mp_spiflash_t spiflash;
 
 void spi_bdev_init(void) {