ppc: Move cpu/$CPU to arch/ppc/cpu/$CPU

Makefile

README

arch/ppc/cpu/74xx_7xx/Makefile

arch/ppc/cpu/74xx_7xx/cache.S

arch/ppc/cpu/74xx_7xx/config.mk

arch/ppc/cpu/74xx_7xx/cpu.c

arch/ppc/cpu/74xx_7xx/cpu_init.c

arch/ppc/cpu/74xx_7xx/interrupts.c

arch/ppc/cpu/74xx_7xx/io.S

arch/ppc/cpu/74xx_7xx/kgdb.S

arch/ppc/cpu/74xx_7xx/speed.c

arch/ppc/cpu/74xx_7xx/start.S

arch/ppc/cpu/74xx_7xx/traps.c

arch/ppc/cpu/mpc512x/Makefile

arch/ppc/cpu/mpc512x/asm-offsets.h

arch/ppc/cpu/mpc512x/config.mk

arch/ppc/cpu/mpc512x/cpu.c

arch/ppc/cpu/mpc512x/cpu_init.c

arch/ppc/cpu/mpc512x/diu.c

arch/ppc/cpu/mpc512x/fixed_sdram.c