net: ti: icssm-prueth: Add support for ICSSM RSTP switch

net: ti: icssm-prueth: Add support for ICSSM RSTP switch

Add support for RSTP switch mode by enhancing the existing ICSSM dual EMAC
driver with switchdev support.

Enable the PRU-ICSSM to operate in switch mode, with the 2 PRU ports acting
as external ports and the host acting as an internal port. Packets received
from the PRU ports will be forwarded to the host (store and forward mode)
and also to the other PRU port (either using store and forward mode or via
cut-through mode). Packets coming from the host will be transmitted either
from one or both of the PRU ports (depending on the FDB decision).

By default, the dual EMAC firmware will be loaded in the PRU-ICSS
subsystem. To configure the PRU-ICSS to operate as a switch, a different
firmware must to be loaded.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Basharath Hussain Khaja <basharath@couthit.com>
Signed-off-by: Parvathi Pudi <parvathi@couthit.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260130124559.1182780-4-parvathi@couthit.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>