net: ti: icssg-prueth: Add ICSSG Ethernet driver for AM65x SR1.0 platforms

Add the PRUeth driver for the ICSSG subsystem found in AM65x SR1.0 devices.
The main differences that set SR1.0 and SR2.0 apart are the missing TXPRU
core in SR1.0, two extra DMA channels for management purposes and different
firmware that needs to be configured accordingly.

Based on the work of Roger Quadros, Vignesh Raghavendra and
Grygorii Strashko in TI's 5.10 SDK [1].

[1]: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/?h=ti-linux-5.10.y

Co-developed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Diogo Ivo <diogo.ivo@siemens.com>
Reviewed-by: MD Danish Anwar <danishanwar@ti.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>