drivers/memory/spiflash: Change to use low-level SPI object not uPy one.

This patch alters the SPI-flash memory driver so that it uses the new
low-level C SPI protocol (from drivers/bus/spi.h) instead of the uPy SPI
protocol (from extmod/machine_spi.h).  This allows the SPI-flash driver to
be used independently from the uPy runtime.
diff --git a/drivers/memory/spiflash.h b/drivers/memory/spiflash.h
index 79ba549..03bad52 100644
--- a/drivers/memory/spiflash.h
+++ b/drivers/memory/spiflash.h
@@ -26,8 +26,8 @@
 #ifndef MICROPY_INCLUDED_DRIVERS_MEMORY_SPIFLASH_H
 #define MICROPY_INCLUDED_DRIVERS_MEMORY_SPIFLASH_H
 
+#include "drivers/bus/spi.h"
 #include "drivers/bus/qspi.h"
-#include "extmod/machine_spi.h"
 
 enum {
     MP_SPIFLASH_BUS_SPI,
@@ -40,7 +40,7 @@
         struct {
             mp_hal_pin_obj_t cs;
             void *data;
-            const mp_machine_spi_p_t *proto;
+            const mp_spi_proto_t *proto;
         } u_spi;
         struct {
             void *data;