KVM: Portability: Move kvm_memory_alias to asm/kvm.h

This patch moves sturct kvm_memory_alias from include/linux/kvm.h
to include/asm-x86/kvm.h. Also have include/linux/kvm.h include
include/asm/kvm.h.

Signed-off-by: Jerone Young <jyoung5@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>