[Death-stack-v4] Add the bsp implementation

.../stm32f767zi_skyward_death_stack_v4/core/stage_1_boot.cpp

...ward_death_stack_v4/interfaces-impl/arch_registers_impl.h

...tm32f767zi_skyward_death_stack_v4/interfaces-impl/bsp.cpp

...2f767zi_skyward_death_stack_v4/interfaces-impl/bsp_impl.h

...f767zi_skyward_death_stack_v4/interfaces-impl/hwmapping.h

...7/stm32f767zi_skyward_death_stack_v4/stm32_2m+16m_xram.ld

...7/stm32f767zi_skyward_death_stack_v4/stm32_2m+384k_ram.ld

...m32f7/stm32f767zi_skyward_death_stack_v4/board_settings.h

miosix/config/boards.cmake

miosix/config/options.cmake