KVM: MMU: move the relevant mmu code to mmu.c

Move the mmu code in kvm_arch_vcpu_init() to kvm_mmu_create()

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>