[auxiliary][WIP] Added support for pyxis auxiliary board

miosix/arch/common/drivers/serial_stm32.cpp

...stm32f429zi_skyward_pyxis_auxiliary/core/stage_1_boot.cpp

...ard_pyxis_auxiliary/interfaces-impl/arch_registers_impl.h

...m32f429zi_skyward_pyxis_auxiliary/interfaces-impl/bsp.cpp

...f429zi_skyward_pyxis_auxiliary/interfaces-impl/bsp_impl.h

...429zi_skyward_pyxis_auxiliary/interfaces-impl/hwmapping.h

...4/stm32f429zi_skyward_pyxis_auxiliary/pyxis_auxiliary.cfg

.../stm32f429zi_skyward_pyxis_auxiliary/stm32_2m+256k_rom.ld

...32f4/stm32f429zi_skyward_pyxis_auxiliary/board_settings.h

miosix/config/boards.cmake

miosix/config/options.cmake