To use this feature a port should define MICROPY_HW_SPIFLASH_SIZE_BITS
along with x_CS, x_SCK, x_MOSI, x_MISO (x=MICROPY_HW_SPIFLASH).  This will
then use external SPI flash on those pins instead of the internal flash.

The SPI is done using the software implementation.  There is currently only
support for standard SPI (ie not dual or quad mode).

Fixes #2806.

stmhal will now be built by default with frozen bytecode from scripts
stored in the stmhal/modules/ directory.  This can be disabled or
changed to another directory by overridding the make variable
FROZEN_MPY_DIR.

This is how CPython does it, and it's very useful to help users discover
the available modules for a given port, especially built-in and frozen
modules.  The function does not list modules that are in the filesystem
because this would require a fair bit of work to do correctly, and is very
port specific (depending on the filesystem).

Ports should no longer use pyhelp_print_obj but instead should define
MICROPY_PY_BUILTINS_HELP to 1 and then specify their help text using
MICROPY_PY_BUILTINS_HELP_TEXT.

This builtin is configured using MICROPY_PY_BUILTINS_HELP, and is disabled
by default.

For a small number of bytes, it's expected to return a small int without
allocation.

This test works only for MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_MPZ
and needs a way of skipping in other cases.

To be implemented later.

If result guaranteedly fits in a small int, it is handled in objint.c.
Otherwise, it is delegated to mp_obj_int_from_bytes_impl(), which should
be implemented by individual objint_*.c, similar to
mp_obj_int_to_bytes_impl().

This makes MicroPython app running in QEMU be pingable from the host (by
following QEMU networking setup instructions,
https://www.zephyrproject.org/doc/samples/net/qemu_setup.html).

In anticipation of enabling more features in the default build. Also, fix
compilation of minimal build.

If, for example, the code-size check failed we would still like to run the
coveralls coverage analysis.