net: atlantic: automatically downgrade the number of queues if necessary

This patch adds support for automatic queue number downgrade.

On A2: this is a must have, because only TC0/TC1 support more than 4Q.
Other TCs support 4Qs maximum.
Thus, on A2 we must downgrade the number of queues per TC to 4, if more
than 2 TCs are requested.

On A1: this allows using 8TCs even on systems with cpu count >= 8, when
we have 8 queues by default.
We will just automatically switch to 8TCx4Q mode in this case.

Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>