core/cpu/boards: removed fw_puts from RIOT

boards/msba2-common/drivers/msba2-uart0.c

boards/redbee-econotag/drivers/redbee_uart.c

core/include/arch/io_arch.h

core/include/io.h

cpu/arm_common/syscalls.c

cpu/atmega2560/io_arch.c

cpu/cc2538/io_arch.c

cpu/lpc1768/io_arch.c

cpu/nrf51822/io_arch.c

cpu/sam3x8e/io_arch.c

cpu/samd21/io_arch.c

cpu/stm32f0/io_arch.c

cpu/stm32f1/io_arch.c

cpu/stm32f3/io_arch.c

cpu/stm32f4/io_arch.c

sys/include/board_uart0.h