Merge branch 'rk3308-gmac'

Tobias Schramm says:

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Add support for RK3308 gmac

The Rockchip RK3308 SoC features an internal gmac. Only the signals
required for RMII are exposed so it is limited to 10/100 Mbit/s operation.
This patchset adds support for it.
I've tested the patchset on a Rock Pi S, works fine.
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Signed-off-by: David S. Miller <davem@davemloft.net>