Merge pull request #4761 from haukepetersen/opt_cpuid

cpu/cc2538/include/cpu_conf.h

cpu/cc2538/include/periph_cpu.h

cpu/cc2538/periph/cpuid.c

cpu/ezr32wg/include/cpu_conf.h

cpu/ezr32wg/include/periph_cpu.h

cpu/ezr32wg/periph/cpuid.c

cpu/k60/include/cpu_conf.h

cpu/k64f/include/cpu_conf.h

cpu/kinetis_common/cpuid.c

cpu/kinetis_common/include/periph_cpu.h

cpu/kw2x/include/cpu_conf.h

cpu/lm4f120/include/cpu_conf.h

cpu/lm4f120/include/periph_cpu.h

cpu/lm4f120/periph/cpuid.c

cpu/lpc11u34/include/cpu_conf.h

cpu/lpc11u34/include/periph_cpu.h

cpu/lpc11u34/periph/cpuid.c

cpu/native/include/cpu_conf.h

cpu/native/include/periph_cpu.h

cpu/native/periph/cpuid.c