This patch allows to completely compile-out support for USB, and no-USB is
now the default. If a board wants to enable USB it should define:
#define MICROPY_HW_ENABLE_USB (1)
And then one or more of the following to select the USB PHY:
#define MICROPY_HW_USB_FS (1)
#define MICROPY_HW_USB_HS (1)
#define MICROPY_HW_USB_HS_IN_FS (1)
This file mirrors py/mpconfig.h but for board-level config options. It
provides a default configuration, to be overridden by a specific
mpconfigboard.h file, as well as setting up certain macros to automatically
configure a board.
Damien George