KVM: PPC: booke: add sregs support

Documentation/kvm/api.txt

arch/powerpc/include/asm/kvm.h

arch/powerpc/include/asm/kvm_44x.h

arch/powerpc/include/asm/kvm_e500.h

arch/powerpc/include/asm/kvm_host.h

arch/powerpc/include/asm/kvm_ppc.h

arch/powerpc/kvm/44x.c

arch/powerpc/kvm/booke.c

arch/powerpc/kvm/e500.c

arch/powerpc/kvm/e500_emulate.c

arch/powerpc/kvm/e500_tlb.c

arch/powerpc/kvm/emulate.c

arch/powerpc/kvm/powerpc.c

include/linux/kvm.h