net: mvneta: Add TC traffic shaping offload

The mvneta controller is able to do some tocken-bucket per-queue traffic
shaping. This commit adds support for setting these using the TC mqprio
interface.

The token-bucket parameters are customisable, but the current
implementation configures them to have a 10kbps resolution for the
rate limitation, since it allows to cover the whole range of max_rate
values from 10kbps to 5Gbps with 10kbps increments.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>