KVM: PPC E500: Add register l1csr0 emulation

Latest kernel start to access l1csr0 to contron L1.
We just tell guest no operation is on going.

Signed-off-by: Liu Yu <yu.liu@freescale.com>
Acked-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>