This is needed for TinyUSB to process USB device IRQs.

Related to #6325.

Signed-off-by: Damien George <damien@micropython.org>

Signed-off-by: Damien George <damien@micropython.org>

The "word" referred to by BYTES_PER_WORD is actually the size of mp_obj_t
which is not always the same as the size of a pointer on the target
architecture.  So rename this config value to better reflect what it
measures, and also prefix it with MP_.

For uses of BYTES_PER_WORD in setting the stack limit this has been
changed to sizeof(void *), because the stack usually grows with
machine-word sized values (eg an nlr_buf_t has many machine words in it).

Signed-off-by: Damien George <damien@micropython.org>

To simplify config, there's no need to specify MP_PLAT_PRINT_STRN if it's
the same as the default definition in py/mpconfig.h.

Signed-off-by: Damien George <damien@micropython.org>

Add "make submodules" to commands when building for the first time.
Otherwise, on a first time build, the submodules have not been checked out
and a lot of `fatal error: nrfx.h: No such file or directory` errors are
printed.

The nrf52840-mdk-usb-dongle and pca10050 comes with a pre-flashed
bootloader (OpenBootloader).

This commit updates the boards "mpconfigboard.mk" to use DFU as
default flashing method and set the corresponding BOOTLOADER
settings such that nrf52840_open_bootloader_1.2.x.ld linker
script is used.

The default DFU flashing method can be disabled by issuing "DFU=0"
when invoking make. This will lead to "segger" being used as default
flashing tool. When using "DFU=0", the linker scripts will not
compensate for any MBR and Bootloader region being present, and might
overwrite them if they were present.

The commit also removes the custom linker script specific to
nrf52840-mdk-usb-dongle as it now points to a generic.

Updated nrf52840-mdk-usb-dongle's README.md to be more clear on
how to deploy the built firmware.

The port README.md has also been updated. In the list of target
boards a new column has been added to indicate which bootloader
is present on the target board. And for consistency, changed all
examples in the README.md to use "deploy" instead of "flash".

An additional Makefile parameter NRFUTIL_PORT can be set in order
to define the serial port to used for the DFU (Default: /dev/ttyACM0).

The "nrfutil" that is used as flasher towards OpenBootloader is
available for installation through Python "pip".

In case of SD=s140, SoftDevice ID 0xB6 is passed to nrfutil's package
generation which corresponds to SoftDevice s140 v6.1.1.

Add the option for "mpconfigboard.mk" to define whether the
board hosts a bootloader or not. The BOOTLOADER make variable
must be set to the name of the bootloader.

When the BOOTLOADER name is set it is also required to supply
the BOOTLOADER_VERSION_MAJOR and the BOOTLOADER_VERSION_MINOR
from the "mpconfigboards.mk". These will be used to resolve which
bootloader linker script that should be passed to the linker.

The BOOTLOADER section also supplies the C-compiler with
BOOTLOADER_<bootloader name>=<version major><version minor>
as a compiler define. This is for future use in case a bootloader
needs to do modification to the startup files or similar (like
setting the VTOR specific to a version of a bootloader).

Adding variables that can be set from other linker scripts:

- _bootloader_head_size:
    Bootloader flash offset in front of the application.

- _bootloader_tail_size:
    Bootloader offset from the tail of the flash.
    In case the bootloader is located at the end.

- _bootloader_head_ram_size:
    Bootloader RAM usage in front of the application.

Updated calculations of application flash and RAM.