[POWERPC] Remove the broken Gemini support

arch/powerpc/kernel/head_32.S

arch/powerpc/platforms/embedded6xx/Kconfig

arch/ppc/Kconfig

arch/ppc/boot/simple/Makefile

arch/ppc/boot/simple/misc.c

arch/ppc/configs/gemini_defconfig

arch/ppc/kernel/head.S

arch/ppc/platforms/Makefile

arch/ppc/platforms/gemini.h

arch/ppc/platforms/gemini_pci.c

arch/ppc/platforms/gemini_prom.S

arch/ppc/platforms/gemini_serial.h

arch/ppc/platforms/gemini_setup.c

arch/ppc/syslib/Makefile

arch/ppc/xmon/start.c

include/asm-ppc/m48t35.h

include/asm-ppc/serial.h