Merge branch 'bcm53134-support'

Álvaro Fernández Rojas says:

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net: dsa: b53: mdio: add support for BCM53134

This is based on the initial work from Paul Geurts that was sent to the
incorrect linux development lists and recipients.
I've modified it by removing BCM53134_DEVICE_ID from is531x5() and therefore
adding is53134() where needed.
I also added a separate RGMII handling block for is53134() since according to
Paul, BCM53134 doesn't support RGMII_CTRL_TIMING_SEL as opposed to is531x5().
====================

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