net: pcs: rzn1-miic: Init RX clock early if MAC requires it

The GMAC1 controller in the RZN1 IP requires the RX MII clock signal to be
started before it initializes its own hardware, thus before it calls
phylink_start.

Implement the pcs_pre_init() callback so that the RX clock signal can be
enabled early if necessary.

Reported-by: Clément Léger <clement.leger@bootlin.com>
Link: https://lore.kernel.org/linux-arm-kernel/20230116103926.276869-4-clement.leger@bootlin.com/
Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240326-rxc_bugfix-v6-7-24a74e5c761f@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>