net: mvpp2: add PPv23 RX FIFO flow control

New FIFO flow control feature was added in PPv23.
PPv2 FIFO polled by HW and trigger pause frame if FIFO
fill level is below threshold.
FIFO HW flow control enabled with CM3 RXQ&BM flow
control with ethtool.
Current  FIFO thresholds is:
9KB for port with maximum speed 10Gb/s port
4KB for port with maximum speed 5Gb/s port
2KB for port with maximum speed 1Gb/s port

Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Acked-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>