ppc4xx: Move gpio.h to ppc4xx-gpio.h since its ppc4xx specific

arch/powerpc/cpu/ppc4xx/cpu_init.c

arch/powerpc/cpu/ppc4xx/gpio.c

arch/powerpc/include/asm/ppc4xx-gpio.h

board/amcc/acadia/memory.c

board/amcc/bamboo/bamboo.c

board/amcc/canyonlands/canyonlands.c

board/amcc/katmai/katmai.c

board/amcc/makalu/makalu.c

board/amcc/sequoia/sequoia.c

board/amcc/taihu/lcd.c

board/amcc/taihu/taihu.c

board/esd/pmc405de/pmc405de.c

board/gdsys/dlvision/dlvision.c

board/gdsys/intip/intip.c

board/korat/korat.c

board/lwmon5/lwmon5.c

board/mosaixtech/icon/icon.c

board/quad100hd/nand.c

board/quad100hd/quad100hd.c

board/t3corp/t3corp.c