The sh_eth_cpu_data::chip_reset() method always resets using ARSTR and
this register is always located at the start of the TSU register region.
Therefore, we can only call this method if we know TSU is there and thus
simplify the probing code a bit...
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be> Signed-off-by: David S. Miller <davem@davemloft.net>