Merge branch 'stmmac-pci-Refactor-DMI-probing'

Jan Kiszka says:

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stmmac: pci: Refactor DMI probing

Some cleanups of the way we probe DMI platforms in the driver. Reduces
a bit of open-coding and makes the logic easier reusable for any
potential DMI platform != Quark.

Tested on IOT2000 and Galileo Gen2.

Changes in v5:
 - fixed a remaining issue in patch 5
 - dropped patch 6 for now
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Signed-off-by: David S. Miller <davem@davemloft.net>