Added port for stm32f769ni_discovery

Makefile

miosix/Makefile

...S/Device/ST/STM32F7xx/Source/Templates/system_stm32f7xx.c

...texM7_stm32f7/stm32f769ni_discovery/core/stage_1_boot.cpp

...m32f769ni_discovery/interfaces-impl/arch_registers_impl.h

...xM7_stm32f7/stm32f769ni_discovery/interfaces-impl/bsp.cpp

..._stm32f7/stm32f769ni_discovery/interfaces-impl/bsp_impl.h

...rtexM7_stm32f7/stm32f769ni_discovery/stm32_2m+16m_xram.ld

...rtexM7_stm32f7/stm32f769ni_discovery/stm32_2m+384k_ram.ld

miosix/config/Makefile.inc

...h/cortexM7_stm32f7/stm32f769ni_discovery/board_settings.h

miosix/config/boards.cmake

miosix/config/options.cmake