ETH: Support physical address auto detection

[P-R-O-C-H-Y]

Description of Change

This PR changes ETH.begin's parameter phy_addr from uint8_t to int32_t to match the eth_phy_config_t.
This also enables using ETH_PHY_ADDR_AUTO as phy_addr in ETH.begin() to automatically get the phy address from the chip.

Tests scenarios

Tested only with SPI Ethernet for now. Will test next week with RMII Ethernet.

Related links

Closes #9311

[github-actions]

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