phy: renesas: Add Renesas Ethernet SERDES driver for R-Car S4-8

Add Renesas Ethernet SERDES driver for R-Car S4-8 (r8a779f0).
The datasheet describes initialization procedure without any information
about registers' name/bits. So, this is all black magic to initialize
the hardware. Especially, all channels should be initialized at once.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20221108005500.3011449-3-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>