octeontx2-af: Quiesce traffic before NIX block reset

[ Upstream commit 762ca6ee ]

During initialization, the AF driver resets all blocks. The RPM (MAC)
block and NIX block operate on a credit-based model. When the NIX block
resets during active traffic flow, it doesn't release credits to the RPM
block. This causes the RPM FIFO to overflow, leading to receive traffic
struck.

To address this issue, the patch introduces the following changes:
1. Stop receiving traffic at the MAC level during AF driver
   initialization.
2. Perform an X2P reset (prevents RXFIFO of all LMACS from pushing data)
3. Reset the NIX block.
4. Clear the X2P reset and re-enable receiving traffic.

Fixes: 54d55781 ("octeontx2-af: Reset all RVU blocks")
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>