net: phy: airoha: air_en8811: use standard rx-polarity/tx-polarity properties

net: phy: airoha: air_en8811: use standard rx-polarity/tx-polarity properties

Replace the proprietary airoha,pnswap-rx / airoha,pnswap-tx boolean
device tree properties with the standard rx-polarity and tx-polarity
properties defined in phy-common-props.yaml.

Backward compatibility is maintained by reading the legacy boolean
properties first and passing them as the default_pol argument to
phy_get_rx/tx_polarity(). If the standard properties are absent the
legacy values are used transparently, so existing device trees remain
functional without modification.

Link: https://git.kernel.org/linus/66d8a334b57e64e43810623b3d88f0ce9745270b
Signed-off-by: Lucien.Jheng <lucienzx159@gmail.com>