SOF irqs are now standard for rx/tx USB transfers, so enable them for both
FS and HS modes.  Fixes #1944.

Added definitions for SPI1, SPI2, and SPI3
Removed USB stuff (that could be removed)
Updated BOARD name defintion

This makes the board match the name printed on the board (and
agree with the documentation)

tools/pydfu.py is now the recommended way of deploying a DFU file.  Old
behaviour of dfu-util can be obtained by passing USE_PYDFU=0 when invoking
make.

The main README.md file has been updated to reflect this change.

To make it easier to spot differences.

Moved from stmhal.

- Put the I2C bus on the corect pins
- Add the appropriate board_init to power the shield

TODO: Probably merge into vfs_fat_diskio.

If None was returned for such requests (which likely means that user simply
didn't handle them), it means successful init and default sector size of 512
bytes respectively. This makes only BP_IOCTL_SEC_COUNT a mandatory request,
and thus re-establishes parity with old interface, where only .count() is
mandatory().

This groups the pins for a port together and puts them in numerical
order. It also adds ARDUINO pin names.

mp_hal_gpio_set_af will search for a given function and unit
and set the alternate function to the alternate function index
found.

This patch adds support to fsusermount for multiple block devices
(instead of just one).  The maximum allowed is fixed at compile time by
the size of the fs_user_mount array accessed via MP_STATE_PORT, which
in turn is set by MICROPY_FATFS_VOLUMES.

With this patch, stmhal (which is still tightly coupled to fsusermount)
is also modified to support mounting multiple devices   And the flash and
SD card are now just two block devices that are mounted at start up if
they exist (and they have special native code to make them more
efficient).

You can now create (singleton) objects representing the flash and SD
card, using:

    flash = pyb.Flash()
    sdcard = pyb.SDCard()

These objects provide the block protocol.

This enables MICROPY_HW_HAS_FLASH which got missed.

The HW has UART2 on the 401 connected to the STLINK procesor
which exposes it as USB serial. This connects that up so that
you can get a REPL using the USB serial.

If MICROPY_FATFS_MAX_SS is defined to power of 2 value between 1024 and
4096, support for dynamic sector size in FatFs will be enabled.  Note
that FatFs reserves static buffer of MICROPY_FATFS_MAX_SS size for each
filesystem in use, so that value should be set sparingly.

Initial patch provided by @pfalcon.

The new block protocol is:
- readblocks(self, n, buf)
- writeblocks(self, n, buf)
- ioctl(self, cmd, arg)

The new ioctl method handles the old sync and count methods, as well as
a new "get sector size" method.

The old protocol is still supported, and used if the device doesn't have
the ioctl method.

Per the previously discussed plan. mount() still stays backward-compatible,
and new mkfs() is rought and takes more args than needed. But is a step
in a forward direction.

If MICROPY_VFS_FAT is defined, mp_type_fileio & mp_type_textio won't be
defined, as these may be alredy defined elsewhere. The idea is to have
compartmentalized VFS FatFs class, which can work in parallel with some
other "main" filesystem. E.g., for unix port, mp_type_fileio, etc. will
be defined for the main POSIX filesystem, while stmhal/file.c will be
a self-contained VFS file class.