sh_eth: Implement ethtool register dump operations

There are many different sets of registers implemented by the
different versions of this controller, and we can only expect this to
get more complicated in future.  Limit how much ethtool needs to know
by including an explicit bitmap of which registers are included in the
dump, allowing room for future growth in the number of possible
registers.

As I don't have datasheets for all of these, I've only included
registers that are:

- defined in all 5 register type arrays, or
- used by the driver, or
- documented in the datasheet I have

Add one new capability flag so we can tell whether the RTRATE
register is implemented.

Delete the TSU_ADRL0 and TSU_ADR{H,L}31 definitions, as they weren't
used and the address table is already assumed to be contiguous.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>