drivers: ethernet: add DSA driver for NXP i.MX NETC

NXP i.MX NETC is a TSN capable Ethernet IP. It may support
ENETC MACs, or/and multiple ports switch.

The ENETC MAC was handled by eth_nxp_imx_netc driver.
This DSA driver is to support NETC switch device.
Current driver supports DSA with limitation that only switch
function is available without management via DSA master port.
DSA master port support is TODO work.

Take i.MX RT1180 NETC hardware as an example.

                +--------+                  +--------+
                | ENETC1 |                  | ENETC0 |
                |        |                  |        |
                | Pseudo |                  |  1G    |
                |  MAC   |                  |  MAC   |
                +--------+                  +--------+
                    | zero copy interface       |
+-------------- +--------+----------------+     |
|               | Pseudo |                |     |
|               |  MAC   |                |     |
|               |        |                |     |
|               | Port 4 |                |     |
|               +--------+                |     |
|           SWITCH       CORE             |     |
+--------+ +--------+ +--------+ +--------+     |
| Port 0 | | Port 1 | | Port 2 | | Port 3 |     |
|        | |        | |        | |        |     |
|  1G    | |  1G    | |  1G    | |  1G    |     |
|  MAC   | |  MAC   | |  MAC   | |  MAC   |     |
+--------+-+--------+-+--------+-+--------+     |
    |          |          |          |          |
NETC External Interfaces (4 switch ports, 1 end-point port)

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>