net: mvpp2: Remove Pause and Asym_Pause support

Packet Processor hardware not connected to MAC flow control unit and
cannot support TX flow control.
This patch disable flow control support.

Fixes: 3f518509

 ("ethernet: Add new driver for Marvell Armada 375 network unit")
Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Acked-by: Marcin Wojtas <mw@semihalf.com>
Link: https://lore.kernel.org/r/1610306582-16641-1-git-send-email-stefanc@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>