phy: renesas: r8a779f0-eth-serdes: Add .power_on() into phy_ops

Add r8a779f0_eth_serdes_power_on() to initialize the hardware for
each channel from the step 9 or later on the datasheet. In other words,
the procedure from the step 1 to 8 is for all channel and it is needed
once only. So, the .init() in any channel instance is called, this
driver initializes the hardware from step 1 to 8. And then, .power_on()
is called, this driver initializes the hardware from step 9 or later.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20221226065316.3895480-2-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>