KVM: x86 emulator: modify 'lods', and 'stos' not to depend on CR2

The current 'lods' and 'stos' is depending on incoming CR2 rather than decode
memory address from registers.

Signed-off-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>