net: ethernet: ti: am65-cpsw: enable DSCP to priority map for RX

net: ethernet: ti: am65-cpsw: enable DSCP to priority map for RX

AM65 CPSW hardware can map the 6-bit DSCP/TOS field to
appropriate priority queue via DSCP to Priority mapping registers
(CPSW_PN_RX_PRI_MAP_REG).

Use a default DSCP to User Priority (UP) mapping as per
https://datatracker.ietf.org/doc/html/rfc8325#section-4.3
and
https://datatracker.ietf.org/doc/html/rfc8622#section-11

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>