KVM: Portability: Move kvm_vcpu_ioctl_get_dirty_log to arch-specific file

Meanwhile keep the interface in common, and leave as more logic in common
as possible.

Signed-off-by: Zhang Xiantao <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

diff --cc drivers/kvm/kvm.h
Simple merge

diff --cc drivers/kvm/kvm_main.c
Simple merge

diff --cc drivers/kvm/x86.c
Simple merge