net: ti: prueth_core: Add support for dumping FW's VLAN/MC table

Add support for userspace to dump VLAN and Multicast filter table
maintained by PRUETH firmware via ethtool IOCTL's register dump
interface.

This is helpful in debugging issues around these filters.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Acked-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>