Merge branch 'sja1110-doc'

Vladimir Oltean says:

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Document the NXP SJA1110 switch as supported

Now that most of the basic work for SJA1110 support has been done in the
sja1105 DSA driver, let's add the missing documentation bits to make it
clear that the driver can be used.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>