[POWERPC] 86xx: Avoid system halt if link training isn't at least L0.

We check the Link Training and State Status register to make sure we
are at least at the L0 state.

Signed-off-by: Zhang Wei <wei.zhang@freescale.com>
Acked-by: Roy Zang <tie-fei.zang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>