powerpc, 8xx: Use IO accessors to access IO memory

arch/powerpc/cpu/mpc8xx/cpu.c

arch/powerpc/cpu/mpc8xx/cpu_init.c

arch/powerpc/cpu/mpc8xx/fec.c

arch/powerpc/cpu/mpc8xx/immap.c

arch/powerpc/cpu/mpc8xx/interrupts.c

arch/powerpc/cpu/mpc8xx/reginfo.c

arch/powerpc/cpu/mpc8xx/serial.c

arch/powerpc/cpu/mpc8xx/speed.c

arch/powerpc/cpu/mpc8xx/spi.c

arch/powerpc/include/asm/iopin_8xx.h

arch/powerpc/lib/time.c

include/watchdog.h