net: renesas: rswitch: use generic MPSM operation for mdio C45

Introduce rswitch_etha_mpsm_op() that accepts values for MPSM register
fields and executes the transaction.

This avoids some code duptication, and can be used both for C45 and C22.

Convert C45 read and write operations to use that.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://patch.msgid.link/20241216071957.2587354-5-nikita.yoush@cogentembedded.com


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