Some boards (like the uGame10) may want to have their own set of extra
modules. This change lets them override EXTRA_BUILTIN_MODULES in their
mpconfigboard.h and makes the ugame10 board do that.
This introduces a new spi_flash_api.h that works for both SPI and
QSPI. The previous spi_flash functions are now called external_flash
to minimize confusion.
There have been multiple uGame prototypes with differences in the pins
and other details. This updates the board definition to fit the final
uGame 10 design.
