net: phy: Add support for driver-specific next update time

Introduce the `phy_get_next_update_time` function to allow PHY drivers
to dynamically determine the time (in jiffies) until the next state
update event. This enables more flexible and adaptive polling intervals
based on the link state or other conditions.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250210082358.200751-2-o.rempel@pengutronix.de


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