[TASK] Remove Linux network driver code

Is there an existing CVA6-SDK task for this?

• I have searched the existing task issues

Task Description

SMSCs PHY's are supported by the upstream kernel, including 8720:

https://elixir.bootlin.com/linux/v5.10/source/drivers/net/phy/smsc.c

They can be enabled with CONFIG_SMSC_PHY.

Description of Done

Remove the network driver and bump kernel version 5.19 (minimum).