arch/arm/include/stm32 and stm32f7: Remove ltdc.h and dma2d.h. Those header...

arch/arm/include/stm32 and stm32f7:  Remove ltdc.h and dma2d.h.  Those header files in that location permitted inclusion into application space logic and, hence, facilitated and encouraged calling into the OS and violating the portable POSIX OS interface.  The definitions in those header files were move the appropriate location in the counterpart, architecture specific files at arch/arm/src/stm32 and stm32f7 dma2d.h and ltdc.h.

configs/stm32f429i-disco/ltdc:  This configuration has been deleted because it violated the portable POSIX OS interface.  It used apps/examples/ltdc and include ltdc.h and dma2d.h which were also removed for the same reason.