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.
The spiflash memory driver is reworked to allow the underlying bus to be
either normal SPI or QSPI. In both cases the bus can be implemented in
software or hardware, as long as the spiflash driver is passed the correct
configuration structure.
The SPI flash driver now supports using an arbitrary SPI object to
communicate with the flash chip, and in particular can use a hardware SPI
peripheral.
