net: ti: icssg-prueth: Add Firmware config and classification APIs.

Add icssg_config.h / .c and icssg_classifier.c files. These are firmware
configuration and classification related files. These will be used by
ICSSG ethernet driver.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>