Merge branch 'stmmac-mt2712-support'

Biao Huang says:

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add Ethernet driver support for mt2712

Changes in v6:
 modifications according to comments from Rob/Andrew/Sean:
 1. use delay_ps instead of delay stage.
 2. add comments in driver to avoid confusion.
 2. rewrite set_delay function.
 3. modify binding document for properties: tx-delay-ps/rx-delay-ps/pericfg etc.
====================

Signed-off-by: David S. Miller <[email protected]>