driver: eth: Support for lan8651 T1S ETH

This patch set provides support for T1S ethernet device - LAN8651.

For SPI communication the implementation of Open Alliance TC6
specification is used.

The driver implementation focuses mostly on reducing memory footprint,
as the used SoC (STM32G491) for development has only 32 KiB RAM in total.

Signed-off-by: Lukasz Majewski <lukma@denx.de>