* Migrate at_at/660m to use new ChibiOS early initialisation code, use generic F072 board.
* Migrate cannonkeys/satisfaction75 to use new ChibiOS early initialisation code, use generic F072 board.
* Migrate nebula12 to use new ChibiOS early initialisation code, use generic F072 board.
* Defer GENERIC_STM32_F072XB board files to ChibiOS.
* Create generic mcuconf.h file for GENERIC_STM32_F072XB.
* Create generic mcuconf.h file for STM32_F103_STM32DUINO.
* Create generic mcuconf.h file for GENERIC_STM32_F042X6.
* Allow boards to override EARLY_INIT_PERFORM_BOOTLOADER_JUMP.
* Initial work for consolidation of board files and default ChibiOS configs.
* Migrate F401/F411 black pills for testing.
* Add early init bootloader jump flag.
* Add support for I2C in order to use i2c_scanner keymap.
* Add F401/F411 HSE bypass to get things booting.
* Exempt "hooked" ChibiOS conf files from updater script.
* Fix up ordering for bootloader_defs file check.
* Match previous $(KEYBOARD_PATHS) value for Proton-C, updated for all board configs.