Merge pull request #7512 from aabadie/cpu_mips_doc

cpu/mips32r2_common/include/cpu.h

cpu/mips32r2_common/include/cpu_conf.h

cpu/mips32r2_common/include/eic_irq.h

cpu/mips_pic32_common/doc.txt

cpu/mips_pic32_common/include/periph_cpu_common.h

cpu/mips_pic32mx/include/cpu.h

cpu/mips_pic32mx/include/cpu_conf.h

cpu/mips_pic32mz/include/cpu.h

cpu/mips_pic32mz/include/cpu_conf.h

cpu/msp430_common/include/cpu.h

cpu/msp430_common/include/cpu_conf.h

cpu/msp430_common/include/msp430_types.h

cpu/msp430_common/include/stdio.h

cpu/msp430_common/include/stdlib.h

cpu/msp430_common/include/sys/stat.h

cpu/msp430_common/include/unistd.h