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.

This driver is imported and adjusted from Linux 6.3-rc1 commit:
50133cd3e8dd1 ("phy: renesas: r8a779f0-eth-serdes: Remove retry code in .init()")

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>