net: ethernet: cortina: Use negotiated TX/RX pause

Instead of directly poking into registers of the PHY, use
the existing function to query phylib about this directly.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240529-gemini-phylib-fixes-v4-2-16487ca4c2fe@linaro.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>