net: ethernet: mtk_eth_soc: improve support for named interrupts

Use platform_get_irq_byname_optional() to avoid outputting error
messages when using legacy device trees which rely identifying
interrupts only by index. Instead, output a warning notifying the user
to update their device tree.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/aeccd00eccb7186d39d2c16292019b3b22ec53b8.1751461762.git.daniel@makrotopia.org


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